Side-by-side simulation · recommended settings
M5 Ultra 256GB vs 512GB: Do local LLMs need 512GB?
Start with 256GB if it completes your workload. Consider 512GB when you need extra room for larger weights, several models or multiple requests.
Choose devices and a model
Expand comparison settings
Same 117output tokens. Only evidence-qualified acceleration is selected automatically; runtime formats are shown on each device.
Left
ReadyStudio M5 Ultra 256GB
Press Start above to generate the same answer on both devices.
Right
ReadyStudio M5 Ultra 512GB
Press Start above to generate the same answer on both devices.
With these settings, total timeis similar on both devices.
Compare from input processing to completion of 117 token response.
Which one fits my needs?
Answer completion
Similar
Total answer time is similar with these settings.
Prompt processing
Similar
Prefill performance is similar at this input length.
Image and video generation
Check the media model
LLM speed does not tell you media-generation performance. Choose the image or video model and resolution separately.
Runtime
Settings for your hardware
oMLX 0.7.0 (4d4f5a28) · mlx-lm 94cdcae · mlx 0.32.2 · native kernels · Lightning MTP on / oMLX 0.7.0 (4d4f5a28) · mlx-lm 94cdcae · mlx 0.32.2 · native kernels · Lightning MTP on. When runtime paths differ, the speed gap also includes software and model-format differences.
Estimated power draw
Studio M5 Ultra 256GB
Estimated LLM power draw is lower at about 300 W. Noise and physical size need a separate check.
Local pricing
Studio M5 Ultra 256GB is about 1,923 × KRW 10,000 cheaper based on the median price. If the speeds are similar, the cheaper one is the balancing choice.
Before choosing hardware
| Measure | Studio M5 Ultra 256GB | Studio M5 Ultra 512GB |
|---|---|---|
| Available fast memory | 236GB | 480GB |
| Memory bandwidth | 1200GB/s | 1200GB/s |
| Estimated total time | 3.6 s | 3.6 s |
| Estimated sustained LLM load | about 300W | about 330W |
| Korean price range (KRW) | 1,850–2,000 × KRW 10,000 | 3,805–3,890 × KRW 10,000 |
Estimated ranges for one user. Multi-GPU and multi-device results depend on the runtime and interconnect.
Decide what you will keep in 512GB together
Capacity depends on whether you run one large model or keep coding, document and embedding models resident together. Budget files plus workspace and KV caches. Pinning only frequently used models is another option. Define that usage plan first to make the reason for 512GB concrete.
Capacity is the key difference for the same model
This pair uses the same M5 Ultra, so compare capacity instead of interpreting memory size as an answer-speed multiplier. Compare one model and input, then select a larger file to see if only one configuration fits it. Check separately whether the larger file improves answers for your workload.
Prepare storage for the model files too
A large memory option still needs SSD space to download and store models. Trying several quantizations can leave multiple copies of one model. Plan the files to retain, cache locations and how to remove unneeded copies so the machine's capacity is used efficiently.