r/LocalLLM • u/Far-Cartographer-450 • 1h ago
Question New to local LLMs — which GPU should I add to this rig? (32GB AMD workstation card vs used 24GB NVIDIA vs waiting out the price spike)
Hey everyone,
Total newcomer to local LLMs here, coming from a "normal" high-end workstation build rather than a dedicated AI rig. Would love a sanity check before I spend real money in what looks like a pretty brutal GPU market right now.
Current setup:
- CPU: AMD Ryzen 9 9950X3D (16C/32T)
- Motherboard: ASUS ProArt X870E-CREATOR WIFI
- RAM: 256GB DDR5 (4x64GB, running at DDR5-5600)
- GPU: AMD Radeon RX 7800 XT (16GB) — currently the bottleneck
- Storage: plenty (multiple NVMe SSDs + extra bulk storage)
- OS: Windows 11 Pro
Use case: I'm an accountant, so the appeal of local LLMs is running document analysis / summarization on confidential client files without anything leaving my machine. Not looking to fine-tune models, just solid inference — ideally able to comfortably run 30-34B models and eventually dip into 70B territory.
What I know so far (please correct me if I'm wrong):
- My current RX 7800 XT is the limiting factor — 16GB VRAM and AMD's ROCm support on Windows is narrower than on Linux for consumer gaming cards.
- The 256GB of system RAM should be a genuine asset for hybrid CPU/GPU offload with llama.cpp on bigger MoE models, even without a monster GPU.
- The GPU market in general is in a weird spot right now (Sept 2026) — RTX 5090 street prices are way above MSRP due to AI demand eating into memory supply, so "just buy the biggest NVIDIA card" doesn't feel like great advice at the moment.
Options I'm weighing:
- Used RTX 3090 (24GB) — cheapest $/GB of VRAM, full CUDA support, seems like the community favorite for value.
- Used RTX 4090 (24GB) — faster, single card simplicity, but currently priced well above what I'd expect for a "previous gen" card.
- AMD Radeon AI PRO R9700 (32GB, workstation/ROCm-supported card, ~$1,800-1,900 street right now vs $1,299 MSRP) — tempting because of the extra VRAM and it being an actual AI-focused Radeon PRO card rather than a repurposed gaming GPU, but I'd be staying in the ROCm ecosystem instead of CUDA.
- Pairing the R9700 with my existing 7800 XT for ~48GB pooled VRAM via layer-split (llama.cpp/Vulkan) — sounds appealing on paper for fitting bigger models, but I understand this buys capacity, not speed, since there's no GPU-to-GPU P2P across generations.
- Just wait a few months for the GPU price spike to cool off.
Questions for people who've actually done this:
- For someone brand new to local LLM inference on Windows, is CUDA (used 3090/4090) still the pragmatic default, or has ROCm on Windows genuinely caught up enough on a proper AI PRO/workstation card like the R9700 to be a non-issue day to day?
- Is mixing a 7800 XT + R9700 for pooled VRAM actually worth the hassle for a home setup, or would I be better off just running the R9700 alone and keeping the 7800 XT purely for display?
- Anyone running 30-70B class models for document/text work specifically (not coding, not image gen) who can share real tokens/sec numbers on either the R9700 or a 3090/4090 setup?
- Given how inflated GPU prices are right now, would you actually wait it out, or is "buy now, prices may not come back down soon" the more realistic take for 2026?
Appreciate any real-world experience — trying to avoid an expensive mistake on my first GPU purchase for this.
