Summary
User reports Qwen3.8-27B Q4 at 50-70 tok/s decode on a borrowed RTX 3090, with the RTX 5080 running ComfyUI at the same time.
The model was loaded entirely on the 3090. The user is deciding between a used RTX 3090, RTX 5090, Mac Studio M5 Ultra 96GB or 256GB, and DGX Spark for a two-user home setup with 1-4 concurrent requests.
Other figures in the post are gathered from benchmarks elsewhere, not measured by the user: RTX 3090 ~40 t/s (~66 with MTP), RTX 5090 ~60-75 t/s, M5 Ultra ~46-48 t/s, DGX Spark ~11-12 t/s (~24 with MTP). The user notes Flash-Next is 125B-A6B plus a ~48GB n-gram table that can live on SSD.