RTX 5080 vs Used RTX 4090 for Local LLMs
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RTX 5080 vs Used RTX 4090 for Local LLMs

RTX 5080 vs used RTX 4090 for local LLMs: 16 GB GDDR7 vs 24 GB GDDR6X, $999 new vs ~$1,200 used. Which delivers the better LLM experience?

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April 24, 2026

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GPU Comparison

GeForce RTX 5080 vs GeForce RTX 4090 for Local LLMs

The RTX 5080 gives you 16 GB of fast GDDR7 with a full warranty. The used 4090 gives you 24 GB of GDDR6X with 1,008 GB/s bandwidth but no warranty. New-gen reliability or extra VRAM?

GeForce RTX 5080

Best New

GeForce RTX 5080

16 GB GDDR7 — Newest Generation

$999.99Check Price
GeForce RTX 4090

Best Used Value

GeForce RTX 4090

24 GB GDDR6X — More VRAM

$1,599.99Check Price

01 / Specifications

Spec by Spec

Specification
GeForce RTX 5080
GeForce RTX 4090
VRAM
16 GB GDDR7
24 GB GDDR6X
Bandwidth
960 GB/s
1,008 GB/s
Architecture
Blackwell
Ada Lovelace
Price
$999 new
~$1,200 used
FP8 Support
Yes
Yes
TDP
360 W
450 W
Recommended PSU
850 W
850 W
Warranty
Full
None (used)
Max Model (full GPU)
13B at Q8
35B at Q4

02 / Model Support

16 GB vs 24 GB: What You Can Run

8 GB more VRAM is the difference between running 7B-13B models and running Mixtral 8x7B, Qwen 32B, and Command R 35B entirely on GPU.

GeForce RTX 5080 — 16 GB

  • Llama 3.1 8B (FP16)

    ~14 GB — Full speed

  • Mistral 7B (Q8)

    ~7 GB — Excellent

  • Phi-3 Medium (Q4)

    ~8 GB — Comfortable

  • 13B models (Q4)

    ~8 GB — Fits well

  • 34B models (Q3)

    ~14 GB — Tight but works

GeForce RTX 4090 — 24 GB

  • Everything from 16 GB

    Plus:

  • Mixtral 8x7B (Q4)

    ~14 GB — Fits well

  • Qwen 2.5 32B (Q4)

    ~18 GB — Comfortable

  • Command R 35B (Q4)

    ~20 GB — Comfortable

  • Llama 70B (Q3)

    ~30 GB — Partial offload

03 / Strengths & Weaknesses

Pros and Cons

GeForce RTX 5080 — Strengths

Strengths

  • Best price-to-performance for 7B-13B model inference
  • GDDR7 bandwidth competitive with much more expensive cards
  • Reasonable 360 W power draw — no PSU upgrade needed for most
  • Full CUDA and Blackwell feature set

Weaknesses

  • 16 GB VRAM limits you to models under ~14B at full precision
  • Cannot run 70B-class models without CPU offloading
  • Less future-proof than 24 GB or 32 GB alternatives

GeForce RTX 4090 — Strengths

Strengths

  • 1,008 GB/s bandwidth — faster than the new RTX 5080
  • 24 GB VRAM opens up 70B-class models
  • Full CUDA + FP8 + Flash Attention support
  • Significant discount over buying new

Weaknesses

  • No warranty on used cards
  • 450 W TDP needs a strong PSU and good cooling
  • Risk of degraded hardware from mining or heavy use

04 / Verdict

The Bottom Line

Best New Card

GeForce RTX 5080

Buy the RTX 5080 if you primarily run 7B-13B models and want the peace of mind of a new card with a full warranty. The 960 GB/s GDDR7 bandwidth means fast token generation for models that fit in 16 GB.

Best for Enthusiasts

GeForce RTX 4090

Buy the used RTX 4090 if you need to run models larger than 16 GB — Mixtral 8x7B, Qwen 32B, Command R 35B. The extra 8 GB of VRAM and higher bandwidth make it the better LLM card. Test on arrival and buy from reputable sellers.

For the full lineup at every budget, see our Best GPU for Local LLMs guide.

05 / Related

More Comparisons

Best GPU Under $1,500

Full lineup at this price point including the RX 7900 XTX.

Best Budget GPUs for LLMs

Full budget guide — VRAM per dollar at every tier.

Best NVIDIA GPUs for LLMs

Full NVIDIA lineup from RTX 3090 to RTX 5090.

Best 24 GB GPUs for LLMs

All 24 GB cards compared — the RTX 4090 leads here.

Frequently Asked Questions

Is 16 GB enough or do I need 24 GB?
16 GB runs 7B-13B models at high quality. 24 GB opens up Mixtral 8x7B, Qwen 32B, and Command R 35B at Q4. If you only use 7B-13B models, 16 GB is fine. For anything larger, the 4090's 24 GB is necessary.
Is the RTX 5080 faster than the RTX 4090?
The 4090 has higher bandwidth (1,008 vs 960 GB/s), so it generates tokens faster for models that fit in both. The 5080 has GDDR7 which is more efficient, but the raw bandwidth advantage goes to the 4090.
Is buying a used RTX 4090 risky?
There is risk: no warranty, potential wear from mining or heavy use. But VRAM is durable. Test under load on arrival, buy from sellers with return policies, and verify VRAM integrity.
Does the RTX 5080 have FP8 support?
Yes, both the 5080 (Blackwell) and 4090 (Ada Lovelace) support FP8. This is not a differentiator between these two cards.

Looking for specific GPU recommendations? Our main guide covers every budget and VRAM tier.

Best GPU for Local LLMs →

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