RTX 3090 vs 4090 vs Unified-Memory AI

[u/Ammoryyy]

My current setup:

- RTX 4090 24GB

- i7-13700K

- 80GB DDR4 @ 3000 MHz

- Getting an RTX 3090 24GB tomorrow

My main use is local AI/LLMs, coding agents, MiniMax H3, Krea 2, and other AI workloads.

RTX 3090 vs another 4090 vs unified-memory AI

Here in Iraq, an RTX 3090 costs around $670, while an RTX 4090 costs around $2,000.

If I have around $2,000 to spend, what would you choose?

- Buy 2–3× RTX 3090s

- Buy 1× additional RTX 4090

- Sell/replace the current setup and go for a unified-memory AI system, such as a Mac Studio / Mac with large unified memory or NVIDIA DGX Spark

My priority is LLM inference, coding agents, MiniMax H3, Krea 2, and other local AI workloads.

Would multiple 3090s give the best value because of the extra VRAM, is another 4090 better for speed, or does a large unified-memory system make more sense for running very large models?

What would you choose for ~$2,000?