Mar 19, 2026

Best GPU for Local LLMs Under $800: Why Buying New Instead of Used Costs You 8 GB of VRAM

At $800, you face the core dilemma in the LLM GPU market: buy a used flagship with 24 GB or a new midrange card with 16 GB. The 8 GB difference is the entire 35B model tier. Here is the math on what each option buys you.

Andre

GPUAILLMs

1.0

The $800 trap explained

New RTX 4070 Ti Super at $800: 16 GB VRAM, 672 GB/s, full warranty Used RTX 3090 at $450: 24 GB VRAM, 936 GB/s, no warranty You pay $350 MORE for 8 GB LESS VRAM and 264 GB/s LESS bandwidth What $350 buys: FP8 support, lower power draw (285 W vs 350 W), and a warranty

For gaming or general compute, the new card is clearly better. For local LLMs, VRAM is the bottleneck that determines which models you can run at all. The used RTX 3090 gives you 50% more VRAM at 43% less cost. The extra 8 GB opens up Mixtral 8x7B (~14 GB), Qwen 2.5 32B (~18 GB), and Command R 35B (~20 GB) - none of which fit in 16 GB at usable quantization. Both Ollama and llama.cpp report real-world token speeds that confirm these bandwidth estimates.

2.0

Options at $800

GPU	VRAM	Price	BW	VRAM/$	Ecosystem	Max Model
Used RTX 3090	24 GB	~$450	936 GB/s	53 MB/$	CUDA	Up to 35B Q4
RTX 4070 Ti Super	16 GB	~$800	672 GB/s	20 MB/$	CUDA	Up to 13B Q8
Used RX 7900 XTX	24 GB	~$650	960 GB/s	37 MB/$	ROCm	Up to 35B Q4

3.0

24 GB vs 16 GB: what the 8 GB gap means

-Fits in 24 GB (not 16 GB): Mixtral 8x7B at Q4 (~14 GB), Qwen 2.5 32B at Q4 (~18 GB), Command R 35B at Q4 (~20 GB), Llama 70B at Q3 (~30 GB, partial offload).
-16 GB covers: all 7B models at any quantization, all 13B models at Q4, 34B models at Q3 (degraded quality), nothing above 34B without heavy offloading.

4.0

Which should you choose?

-Used RTX 3090 (~$450): Best choice for LLMs at this budget. 24 GB CUDA at the lowest price. You sacrifice warranty and FP8 for 50% more VRAM and 39% more bandwidth vs the 4070 Ti Super.
-RTX 4070 Ti Super (~$800): Choose this only if you run 7B-13B models exclusively and want new-card reliability. The 672 GB/s bandwidth is adequate for smaller models.
-Used RX 7900 XTX (~$650): Middle ground. 24 GB at a moderate price, but ROCm adds software friction. Only if you are comfortable with AMD on Linux.

For GPU options at other budgets, see Best GPU for Local LLMs. Use our VRAM Calculator to verify your target model fits your budget card's VRAM.

FAQ

Frequently Asked Questions

Is a used RTX 3090 reliable enough for daily LLM use?

Generally yes. VRAM is durable, and GDDR6X degradation is extremely rare. The main risk is fan failure (cheap to replace) or thermal paste drying (easy to reapply). Buy from sellers with return policies and test VRAM on arrival.

Can I find a used RX 7900 XTX under $800?

Yes, used 7900 XTX cards sell for $600-700. That gives you 24 GB with ROCm. A strong value if you are comfortable with AMD software and run Linux.

What models can I realistically run under $800?

With a used 24 GB card: Mixtral 8x7B, Qwen 32B, Command R 35B at Q4, and 70B at Q3 with offloading. With a new 16 GB card: 7B-13B at high quality, 34B at Q3.

End of Document