Mac Studio (2025) M3 Ultra 96GB vs 2x RTX 3090 (48GB total) for local LLMs
Memory fit, speed and context compared with the same math as the advisor. Mac Studio (2025) M3 Ultra 96GB has 20.7 GB more usable memory (66.7 vs 46.0 GB) and higher bandwidth than the other (819 vs 936 GB/s).
Verdict from the numbers
- Fit. Mac Studio (2025) M3 Ultra 96GB fits 12 of 13 models fully at 16k context (largest: gpt-oss 120B Q8_0); 2x RTX 3090 (48GB total) fits 11 (largest: Qwen3.6 35B-A3B Q8_0). Only Mac Studio (2025) M3 Ultra 96GB fits fully: gpt-oss 120B.
- Speed. On the 11 models that fit fully on both, 2x RTX 3090 (48GB total) is faster by a typical 1.8x. Mac Studio (2025) M3 Ultra 96GB is ahead on 0, 2x RTX 3090 (48GB total) on 11. No model is measured on both machines, so every comparison involves an estimate; read it as a guide.
- Trade-off. Mac Studio (2025) M3 Ultra 96GB has 20.7 GB more usable memory (66.7 vs 46.0 GB) and higher bandwidth than the other (819 vs 936 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: Mac Studio (2025) M3 Ultra 96GB has 20.7 GB more usable memory, which moves 1 of 13 models into full-GPU fit (gpt-oss 120B). 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 | Mac Studio (2025) M3 Ultra 96GB fit | tok/s | 2x RTX 3090 (48GB total) fit | tok/s | Faster / fits |
|---|---|---|---|---|---|
| Gemma 4 26B-A4B Q8_0 | fits fully | 63 estimated | fits fully | 125 estimated | 2x RTX 3090 (48GB total) |
| Gemma 4 31B Q4_K_M | fits fully | 18 estimated | fits fully | 19 estimated | 2x RTX 3090 (48GB total) |
| Gemma 4 12B Q8_0 | fits fully | 24 scaled from measured | fits fully | 49 estimated | 2x RTX 3090 (48GB total) |
| Qwen3.6 27B Q5_K_M | fits fully | 17 estimated | fits fully | 22 estimated | 2x RTX 3090 (48GB total) |
| Qwen3.6 35B-A3B Q8_0 | fits fully | 83 estimated | fits fully | 163 estimated | 2x RTX 3090 (48GB total) |
| Qwen3.5 9B Q8_0 | fits fully | 34 scaled from measured | fits fully | 67 estimated | 2x RTX 3090 (48GB total) |
| Qwen3.5 4B Q8_0 | fits fully | 68 scaled from measured | fits fully | 143 estimated | 2x RTX 3090 (48GB total) |
| gpt-oss 20B Q8_0 | fits fully | 115 scaled from measured | fits fully | 241 estimated | 2x RTX 3090 (48GB total) |
| gpt-oss 120B Q8_0 | fits fully | 92 estimated | MoE offload to CPU | 55 estimated | Mac Studio (2025) M3 Ultra 96GB (fits) |
| Qwen3-Coder 30B-A3B Q8_0 | fits fully | 73 estimated | fits fully | 143 estimated | 2x RTX 3090 (48GB total) |
| Mistral Small 3.2 24B Q6_K | fits fully | 17 estimated | fits fully | 26 estimated | 2x RTX 3090 (48GB total) |
| Qwen3-VL 8B Q8_0 | fits fully | 37 scaled from measured | fits fully | 74 estimated | 2x RTX 3090 (48GB total) |
| GLM-4.5-Air Q4_K_M | does not fit | - | MoE offload to CPU | 14 estimated | - |
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 | Mac Studio (2025) M3 Ultra 96GB f16 | 2x RTX 3090 (48GB total) f16 | Mac Studio (2025) M3 Ultra 96GB q8_0 | 2x RTX 3090 (48GB total) q8_0 |
|---|---|---|---|---|
| gpt-oss 120B | 64k | - | 128k | - |
| Qwen3.6 35B-A3B | 1M | 256k | 1M | 512k |
| Gemma 4 31B | 256k | 128k | 256k | 256k |
| Qwen3-Coder 30B-A3B | 256k | 128k | 512k | 128k |
| Qwen3.6 27B | 512k | 256k | 1M | 256k |
| Gemma 4 26B-A4B | 256k | 256k | 256k | 256k |
| Mistral Small 3.2 24B | 128k | 64k | 128k | 128k |
| gpt-oss 20B | 128k | 128k | 128k | 128k |
| Gemma 4 12B | 256k | 256k | 256k | 256k |
| Qwen3.5 9B | 1M | 1M | 1M | 1M |
| Qwen3-VL 8B | 256k | 128k | 512k | 256k |
| Qwen3.5 4B | 1M | 1M | 1M | 1M |
Spec summary
| Mac Studio (2025) M3 Ultra 96GB | 2x RTX 3090 (48GB total) | |
|---|---|---|
| Usable memory for model + KV cache | 66.7 GB | 46.0 GB |
| Memory bandwidth | 819 GB/s | 936 GB/s |
| Models that fit fully at 16k | 12 of 13 | 11 of 13 |
| Models that need offload or do not fit | 1 | 2 |
| Measured data points on file | 5 | none (multi-GPU is estimated) |
FAQ
Which is faster for local LLMs, Mac Studio (2025) M3 Ultra 96GB or 2x RTX 3090 (48GB total)?
On the 11 models that fit fully on both, 2x RTX 3090 (48GB total) is typically 1.8x faster (geometric mean). Mac Studio (2025) M3 Ultra 96GB wins 0 and 2x RTX 3090 (48GB total) wins 11. 0 comparisons are measured on both.
Which fits more models, Mac Studio (2025) M3 Ultra 96GB or 2x RTX 3090 (48GB total)?
Mac Studio (2025) M3 Ultra 96GB fits 12 of 13 models fully at 16k context and 2x RTX 3090 (48GB total) fits 11. Only Mac Studio (2025) M3 Ultra 96GB: gpt-oss 120B.
Can I run long context on Mac Studio (2025) M3 Ultra 96GB or 2x RTX 3090 (48GB total)?
At f16 KV cache, the largest-model context limits are in the table above (for example gpt-oss 120B on Mac Studio (2025) M3 Ultra 96GB: 64k; Qwen3.6 35B-A3B on 2x RTX 3090 (48GB total): 256k). A q8_0 KV cache extends it further.
Do you state prices for Mac Studio (2025) M3 Ultra 96GB or 2x RTX 3090 (48GB total)?
No. Prices change daily, so we link to Amazon search results instead and focus on measured and estimated speed and memory fit.
Related
Mac Studio (2025) M3 Ultra 96GB · 2x RTX 3090 (48GB total)
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