RTX 3090 24GB vs AMD RX 7900 XTX 24GB for local LLMs
Memory fit, speed and context compared with the same math as the advisor. Both offer about the same usable memory (23.0 GB), so the difference is mostly bandwidth (936 vs 960 GB/s).
Verdict from the numbers
- Fit. RTX 3090 24GB fits 11 of 13 models fully at 16k context (largest: Qwen3.6 35B-A3B UD-Q4_K_M); AMD RX 7900 XTX 24GB fits 11 (largest: Qwen3.6 35B-A3B UD-Q4_K_M). Both fit the same set of models.
- Speed. On the 11 models that fit fully on both, RTX 3090 24GB is faster by a typical 1.3x. RTX 3090 24GB is ahead on 6, AMD RX 7900 XTX 24GB on 5. No model is measured on both machines, so every comparison involves an estimate; read it as a guide.
- Trade-off. Both offer about the same usable memory (23.0 GB), so the difference is mostly bandwidth (936 vs 960 GB/s).
Where to check prices
Price tier note
We do not list prices because they move daily and differ between new and used stock. What the data does show is what the memory difference buys: both have the same usable memory, so model fit is identical and the choice comes down to speed (936 vs 960 GB/s bandwidth). Use the Amazon links above to compare current listings and decide whether the difference is worth it for the models you want to run.
Model by model · 16k context, f16 KV cache
| Model | RTX 3090 24GB fit | tok/s | AMD RX 7900 XTX 24GB fit | tok/s | Faster / fits |
|---|---|---|---|---|---|
| Gemma 4 26B-A4B UD-Q5_K_M | fits fully | 112 scaled from measured | fits fully | 147 estimated | AMD RX 7900 XTX 24GB |
| Gemma 4 31B Q4_K_M | fits fully | 39 measured | fits fully | 40 scaled from measured | AMD RX 7900 XTX 24GB |
| Gemma 4 12B Q8_0 | fits fully | 57 measured | fits fully | 45 scaled from measured | RTX 3090 24GB |
| Qwen3.6 27B Q5_K_M | fits fully | 36 scaled from measured | fits fully | 30 scaled from measured | RTX 3090 24GB |
| Qwen3.6 35B-A3B UD-Q4_K_M | fits fully | 159 measured | fits fully | 248 estimated | AMD RX 7900 XTX 24GB |
| Qwen3.5 9B Q8_0 | fits fully | 86 measured | fits fully | 25 scaled from measured | RTX 3090 24GB |
| Qwen3.5 4B Q8_0 | fits fully | 138 measured | fits fully | 46 scaled from measured | RTX 3090 24GB |
| gpt-oss 20B Q8_0 | fits fully | 204 measured | fits fully | 219 estimated | AMD RX 7900 XTX 24GB |
| gpt-oss 120B | does not fit | - | does not fit | - | - |
| Qwen3-Coder 30B-A3B Q4_K_M | fits fully | 206 measured | fits fully | 228 estimated | AMD RX 7900 XTX 24GB |
| Mistral Small 3.2 24B Q6_K | fits fully | 37 scaled from measured | fits fully | 30 scaled from measured | RTX 3090 24GB |
| Qwen3-VL 8B Q8_0 | fits fully | 91 scaled from measured | fits fully | 28 scaled from measured | RTX 3090 24GB |
| GLM-4.5-Air | does not fit | - | does not fit | - | - |
Badges: measured medians of real llama.cpp runs; scaled from measured and estimated come from our bandwidth model. See sources and methods.
How much context fits?
Largest context where weights plus KV cache stay inside usable memory, per model that fits fully on at least one side. q8_0 KV roughly halves the cache.
| Model | RTX 3090 24GB f16 | AMD RX 7900 XTX 24GB f16 | RTX 3090 24GB q8_0 | AMD RX 7900 XTX 24GB q8_0 |
|---|---|---|---|---|
| Qwen3.6 35B-A3B | 32k | 32k | 64k | 64k |
| Gemma 4 31B | 32k | 32k | 64k | 64k |
| Qwen3-Coder 30B-A3B | 32k | 32k | 64k | 64k |
| Qwen3.6 27B | 32k | 32k | 64k | 64k |
| Gemma 4 26B-A4B | 64k | 64k | 128k | 128k |
| Mistral Small 3.2 24B | 16k | 16k | 32k | 32k |
| gpt-oss 20B | 128k | 128k | 128k | 128k |
| Gemma 4 12B | 256k | 256k | 256k | 256k |
| Qwen3.5 9B | 256k | 256k | 512k | 512k |
| Qwen3-VL 8B | 64k | 64k | 128k | 128k |
| Qwen3.5 4B | 512k | 512k | 1M | 1M |
Spec summary
| RTX 3090 24GB | AMD RX 7900 XTX 24GB | |
|---|---|---|
| Usable memory for model + KV cache | 23.0 GB | 23.0 GB |
| Memory bandwidth | 936 GB/s | 960 GB/s |
| Models that fit fully at 16k | 11 of 13 | 11 of 13 |
| Models that need offload or do not fit | 2 | 2 |
| Measured data points on file | 20 | 8 |
FAQ
Which is faster for local LLMs, RTX 3090 24GB or AMD RX 7900 XTX 24GB?
On the 11 models that fit fully on both, RTX 3090 24GB is typically 1.3x faster (geometric mean). RTX 3090 24GB wins 6 and AMD RX 7900 XTX 24GB wins 5. 0 comparisons are measured on both.
Which fits more models, RTX 3090 24GB or AMD RX 7900 XTX 24GB?
RTX 3090 24GB fits 11 of 13 models fully at 16k context and AMD RX 7900 XTX 24GB fits 11.
Can I run long context on RTX 3090 24GB or AMD RX 7900 XTX 24GB?
At f16 KV cache, the largest-model context limits are in the table above (for example Qwen3.6 35B-A3B on RTX 3090 24GB: 32k; Qwen3.6 35B-A3B on AMD RX 7900 XTX 24GB: 32k). A q8_0 KV cache extends it further.
Do you state prices for RTX 3090 24GB or AMD RX 7900 XTX 24GB?
No. Prices change daily, so we link to Amazon search results instead and focus on measured and estimated speed and memory fit.
Related
RTX 3090 24GB · AMD RX 7900 XTX 24GB · Measured model pages: gpt-oss 20B · Qwen3.6 35B-A3B · Qwen3-Coder 30B-A3B · Gemma 4 31B · Qwen3.6 27B · Gemma 4 26B-A4B
More comparisons: RTX 3090 24GB vs RTX 4090 24GB · RTX 3090 24GB vs RTX 5090 32GB · RTX 4090 24GB vs AMD RX 7900 XTX 24GB · all comparisons
By memory: 8 GB · 12 GB · 16 GB · 24 GB · 32 GB · 48 GB · 64 GB · 96 GB · 128 GB · 192 GB · 256 GB · 512 GB