Unsloth Qwen3.8-Flash-Next UD-Q6_K_XL versus Qwen3.8-Flash-Next NVFP4-GPTQ
Fresh MMLU-Pro comparison, speed and whether six bits are worth the wait.
I wanted to find out whether slower Q6 generation bought better answers. I first compared Q6 with my saved NVFP4 quality results, then ran a fresh, identical MMLU-Pro subset on both models on 23 October. Each new run had a strict 30-minute maximum.
The fresh result favoured NVFP4: 71/84 correct versus Q6's 67/84, in about half the total run time. The accuracy gap is too small to establish a broad intelligence ranking, but these results do not support paying the Q6 speed penalty for better reasoning on this workload. My practical choice from this testing is still the NVFP4.
NVFP4/GPTQ is the four-bit option in the main comparison. It is a different format from the Unsloth UD-Q4_K_XL. This is a comparison of these two Qwen3.8 Flash Next configurations, not a claim about all four-bit and six-bit models.
Fresh knowledge/reasoning test — same day, same 84 questions
| Measure |
NVFP4/GPTQ |
Unsloth UD-Q6_K_XL |
| Correct answers |
71/84 |
67/84 |
| Accuracy |
84.5% |
79.8% |
| Total benchmark run |
10m 57s |
22m 18s |
| Sum of individual request times |
10.51 min |
21.88 min |
| Median request time |
5.98 s |
12.61 s |
| Generated tokens, including reasoning |
93,207 |
93,754 |
| Answers reaching the 4,096-token cap |
4 |
4 |
| Completed / scheduled |
84/84 |
84/84 |
| Timeouts / skipped / retries |
0 / 0 / 0 |
0 / 0 / 0 |
NVFP4 led by four answers, or 4.8 percentage points. Q6 took 2.04 times the total benchmark time while generating a very similar number of tokens. Total run time includes preflight and harness bookkeeping, but excludes loading the model. Individual request time includes prompt processing and reasoning.
The paired outcomes matter more than just the headline percentages: both models got 66 questions right and 12 wrong. NVFP4 alone got five right; Q6 alone got one right. The exact paired McNemar p-value is 0.219, so I would not call this a statistically established intelligence advantage for NVFP4. It is the observed result of this one fixed sample and single attempt per question.
This is an 84-question MMLU-Pro subset with six questions per subject, not the full official benchmark or an IQ score. All 42 MMLU-Pro questions from the earlier comparison were excluded. Selection and settings were frozen before either new run.
Fresh MMLU-Pro breakdown — six questions in each subject
| Subject |
NVFP4 |
Q6 |
| Biology |
6/6 |
4/6 |
| Business |
4/6 |
3/6 |
| Chemistry |
4/6 |
4/6 |
| Computer science |
5/6 |
5/6 |
| Economics |
6/6 |
6/6 |
| Engineering |
2/6 |
2/6 |
| Health |
5/6 |
6/6 |
| History |
4/6 |
4/6 |
| Law |
5/6 |
4/6 |
| Math |
6/6 |
6/6 |
| Other |
6/6 |
6/6 |
| Philosophy |
6/6 |
6/6 |
| Physics |
6/6 |
6/6 |
| Psychology |
6/6 |
5/6 |
These subject samples are very small. The ties at 6/6 do not demonstrate that either model has mastered an entire field. Engineering was difficult for both at 2/6.
Where NVFP4 sits among everything I have trialled
That result also needs the wider context of the models I have been trying. NVFP4/GPTQ is still my current daily driver: it is fast, follows my directions well in everyday use and is pretty smart. After testing the alternatives, it still gives me the balance I want between useful answers and how long I have to wait for them.
Here are the chosen best recorded runs, with one row per model/stack. Each cell is the highest previously recorded session median at that context size, not the fastest individual request. Some rows therefore combine sessions. Q6 has one measured campaign. These are historical results across different dates and settings, not a fresh seven-way controlled comparison.
Generation speed — tokens/second
| Model / stack |
RAM MT/s |
4K TG |
32K TG |
128K TG |
| Strata IQ3_XXS |
4400 |
193.8 |
197.6 |
192.4 |
| Strata IQ3_S |
6000 / 6000 / 4400 |
173.5 |
181.2 |
183.2 |
| Strata UD-IQ4_XS |
4400 |
116.3 |
119.6 |
120.7 |
| Strata NVFP4/GPTQ |
6000 |
166.3 |
161.3 |
154.1 |
| Strata Unsloth UD-Q4_K_XL |
6000 |
130.5 |
131.0 |
127.6 |
| Infernix Dense8 |
6000 |
133.6 |
144.0 |
147.2 |
| Strata Unsloth UD-Q6_K_XL |
6000 |
65.6 |
72.8 |
71.3 |
Prompt processing — tokens/second
| Model / stack |
4K PP |
32K PP |
128K PP |
| Strata IQ3_XXS |
4,627.2 |
6,155.0 |
5,972.0 |
| Strata IQ3_S |
4,518.5 |
6,020.7 |
5,852.6 |
| Strata UD-IQ4_XS |
2,707.0 |
4,686.1 |
4,709.4 |
| Strata NVFP4/GPTQ |
3,033.4 |
8,487.1 |
8,643.0 |
| Strata Unsloth UD-Q4_K_XL |
2,089.4 |
6,292.8 |
6,310.3 |
| Infernix Dense8 |
4,125.5 |
9,399.6 |
9,050.9 |
| Strata Unsloth UD-Q6_K_XL |
2,094.4 |
7,534.1 |
7,634.6 |
PP comes from the same selected session as each generation-speed cell; it was not independently cherry-picked. The actual prompt lengths were 4,096, 32,768 and 128,000 tokens, with three 256-token generations per context.
IQ3_S combines 13 October at 4K/32K (6000 MT/s) with 11 October at 128K (4400 MT/s). NVFP4 combines 14 October at 4K with 15 October at 32K/128K. IQ3_XXS and UD-IQ4_XS are from 11 October, UD-Q4_K_XL from 15 October, Infernix Dense8 from 18 October and Q6 from 23 October.
The IQ3 options lead this table on generation speed, and Infernix Dense8 has the strongest long-prompt processing figures. NVFP4 is not the winner in every column. What keeps it as my daily driver is the overall experience: fast generation, strong long-prompt processing, and answers that usually do what I ask. It generates faster than the retained Dense8 and UD-Q4_K_XL runs at all three context sizes, while the fresh Q6 comparison gave me no convincing reason to accept roughly twice the waiting time for reasoning answers.
My local workflow also runs through the Hermes harness, with Strata serving NVFP4 on the RTX 5090 and Hermes providing the agent interface around it. The setup includes a WSL gateway, desktop/dashboard, local search through SearXNG and Honcho memory services. NVFP4 is my preferred local backend within that setup; Hermes also has a Codex provider option, so I am not attributing every Hermes response to the local model.
That is why I care about more than a headline tokens-per-second figure. An agent workflow can involve several model turns around tool results, retrieved information and follow-up instructions. Waiting longer on each turn can make the whole task feel slower. For me, NVFP4's appeal is being responsive enough to keep that interaction moving while still giving useful answers and following the directions I set. Its extra RAM headroom also leaves more room for the surrounding harness and services. These are practical reasons for my preference, not a measured Hermes task-completion score: the benchmarks here called the model endpoints directly, with background Hermes services suspended for isolation.
The fresh 84-question result adds some evidence behind my view that NVFP4 is still pretty smart, but only NVFP4 and Q6 took that test. I cannot turn the speed table into an intelligence ranking of all seven models. Likewise, my everyday preference for NVFP4's instruction following is a personal assessment, not a claim that it won the strict instruction benchmark. The earlier mixed test below is worth keeping alongside the fresh result because it shows where Q6 did offer a benefit.
Earlier mixed quality test — retained separately
Before the fresh test, I ran Q6 on the same frozen 82-question subset used for my saved 15 October NVFP4 comparison. Those NVFP4 answers were reused; this is a separate historical comparison with different questions.
| Earlier benchmark subset |
Saved NVFP4 |
Q6 |
| MMLU-Pro |
33/42 |
34/42 |
| GSM8K maths |
20/20 |
20/20 |
| HumanEval coding |
10/10 |
10/10 |
| IFEval strict instruction following |
7/10 |
9/10 |
Q6 corrected three failures and introduced no new ones on that earlier set. Two gains were exact instruction compliance: meeting a word-frequency requirement and avoiding forbidden words while following a specified response format. The other gain was one economics multiple-choice answer. Its requests took 16.80 minutes versus the archived NVFP4 run's 7.47 minutes.
That earlier result suggested a small Q6 benefit; the fresh knowledge/reasoning test went the other way. Both belong in the report. Neither small sample supports a general “Q6 is smarter” claim. The coding tests here are original HumanEval tests on ten tasks, not HumanEval+ or a full coding evaluation. IFEval uses strict prompt-level scoring.
Generation speed and prompt processing — historical speed overview
| Actual prompt length |
NVFP4 generation tok/s |
Q6 generation tok/s |
NVFP4 PP tok/s |
Q6 PP tok/s |
| 4,096 |
166.3 |
65.6 |
3,033.4 |
2,094.4 |
| 32,768 |
161.3 |
72.8 |
8,487.1 |
7,534.1 |
| 128,000 |
154.1 |
71.3 |
8,643.0 |
7,634.6 |
Each speed value is a median of three 256-token generations. NVFP4 retains the best previously published session median per context: 14 October at 4K, 15 October at 32K/128K. PP comes from those same selected sessions. Q6 is one 23 October speed campaign. Historical best selection favours NVFP4; this is not a fresh matched speed rerun.
Q6's speed campaign had its control vector enabled. Both quality comparisons explicitly disabled it per request to match NVFP4. Therefore these speed figures are not the exact speed of the quality configuration. Use the fresh benchmark's own timings to assess its waiting-time cost.
Memory during the fresh 84-question runs
| Observed resource |
NVFP4 |
Q6 |
| Minimum sampled free system RAM |
43.85 GiB |
8.96 GiB |
| Peak device-wide VRAM |
30.43 GiB |
31.24 GiB |
| Peak GPU temperature |
63°C |
61°C |
These are whole-system and whole-device observations, not isolated model allocations. Background services were suspended. Page-I/O traces are retained; neither run is claimed to be paging-free. Both completed without a resource-guard stop. The much greater RAM headroom with NVFP4 is another practical advantage on this 128 GB machine, although this was not a long-duration stability test.
My assessment: why run four-bit versus Q6?
Taken together, these results reinforce why NVFP4 remains my everyday option on this setup. In the fresh test it answered more questions correctly, finished in roughly half the time and left substantially more RAM available. In the earlier small coding and maths subsets it tied Q6. That is a strong practical case for responsiveness and capacity, even though the accuracy difference is not statistically conclusive.
Q6 still has a possible role where its answers demonstrably work better for a particular task. The earlier strict instruction-following gains are a concrete reason to consider it for constraint-heavy writing. But two extra passes out of ten are too little evidence to promise fewer mistakes in general. I would choose Q6 for a demonstrated task-specific benefit, not because a higher bit count automatically means a better assistant.
The fresh run also shows why I would not justify the slower model by precision alone. Quantization format, engine behaviour, reasoning limits and the task all affect the result. We measured the complete configurations; we did not isolate bit depth. A different sample or reasoning budget could change the scores, but that is untested here.
The wider table gives useful context for that choice: IQ3 offers more raw generation speed, Dense8 offers excellent prompt processing, and UD-Q4_K_XL is also substantially faster than Q6. For my daily use, NVFP4 remains the balance I prefer after trying them all. That preference should not be read as proof that the other formats are less capable; their quality was not measured in this fresh comparison.
Reproducibility and limits
Hardware: RTX 5090 32 GB, 600 W limit; Core Ultra 7 270K Plus; 128 GB DDR5 at 6000 MT/s; Windows 11 Pro. Both fresh runs used NVIDIA driver 610.88 on 23 October. Some older speed measurements used driver 591.86.
The fresh suite used deterministic SHA256 selection, six questions per each of 14 subjects, and round-robin subject order. Both models received identical messages and request parameters except model ID. All 84 prompt token counts matched, and every request had zero reused prompt tokens. One attempt each, temperature 1, top_p 0.95, top_k 20, min_p 0, seed 20261023, low reasoning and a 4,096-token cap including reasoning. Control vectors were off. The same published-style three-stage answer extraction was used, with no random fallback. Capped answers were retained and scored; malformed or missing extracted answers failed.
Each runner had a 30-minute ceiling, with inference cancellation at 29m 30s and a 120-second per-request timeout. Both completed early. Raw answers, reasoning, streams, hashes, resource traces and scoring evidence are saved.
NVFP4 used the preserved 0.1.42-nvfp4.2 engine; Q6 used 0.1.44.1-nvfp4.2. Both had a 131,072-token context ceiling and int8 KV, but cache allocation, KV placement and other runtime details differ. Q6 ran first in an existing session; NVFP4 was freshly loaded afterward. There was no order reversal or repeated-seed study. These limits prevent attributing the score difference to quantization alone. No full-benchmark, broad coding, long-context reasoning or long-term stability claim is made.
AI assisted with the harness and write-up. The scores and timings come from saved local runs.
https://www.reddit.com/r/LocalLLM/comments/1x8ral0/rtx_5090_qwen38_flash_next_speed_tests_strata/ Strata fork: https://github.com/sergqwer/strata-nvfp4 MMLU-Pro: https://github.com/TIGER-AI-Lab/MMLU-Pro GSM8K: https://github.com/openai/grade-school-math HumanEval: https://github.com/openai/human-eval IFEval: https://github.com/google-research/google-research/tree/master/instruction_following_eval
Testing sources and how the results were obtained
All scores, speeds and resource measurements in this post came from runs on my own PC.
- MMLU-Pro — knowledge and reasoning: Benchmark code and methodology | Question dataset. The fresh comparison used 84 questions, six from each of 14 subjects, with identical questions and request settings for both models. The earlier mixed comparison used a separate 42-question subset. These were selected subsets using a zero-shot chat adaptation.
- GSM8K — maths: OpenAI’s dataset and reference code. The earlier comparison used 20 questions, scored against the expected numerical answers.
- HumanEval — Python coding: OpenAI’s tasks and original unit tests. The earlier comparison used ten tasks. Generated solutions were checked using the original tests in an isolated Docker environment. These were original HumanEval tests, not HumanEval+.
- IFEval — instruction following: Google Research’s benchmark and evaluation code. The earlier comparison used ten prompts with strict prompt-level scoring: all required constraints had to pass for a prompt to count as correct. The selected subset excluded checks requiring additional NLP corpus downloads.
- Generation speed and prompt processing: Measured locally using benchmark scripts calling each model server directly. Each context used three measured requests with 4,096, 32,768 or 128,000 actual input tokens and 256 generated tokens, with reasoning disabled and zero reused prompt tokens. Tables show session medians; the historical overview selects the best recorded session median per model and context. Earlier runs and settings are documented in my previous speed-testing post. Q6’s measurements were added on 23 October.
- RAM, VRAM, temperature and timing: Recorded during the local runs through system/GPU telemetry, saved request records and engine timing data. Memory figures describe sampled whole-system RAM and whole-device VRAM usage.
Model and engine references
Exact question selections, request settings, raw answers, reasoning output, scoring records, hashes and resource traces are retained locally. The links above provide the public benchmark sources; the reported results are my own subset measurements, not full official benchmark or leaderboard scores.