Qwen3.8 125B (6B active) Flash-Next

User reports 25-29 t/s decode at short and mid context on 2x RTX 3090 over PCIe 3.0 with dual Xeon E5-2696 v4 and 188 GB usable DDR4-2133 LRDIMM, up from ~17 t/s before. Setup is llama.cpp with the Qwen3.8-Flash-Next UD-Q6_K_XL GGUF, f16 KV cache, full 261,888 context, all 48 expert layers pinned in host RAM and everything else on GPUs, using PR #27861 GPU-resident LRU expert cache with 135 cache slots per layer. Decode holds ~17 t/s at 131k depth, prefill is unchanged at ~350 t/s on a 26k prompt, and the cache hit rate is 80-85% on code. Dropping ubatch from 2048 to 512 freed ~5 GB per GPU, and prefill is slower on long prompts. Thread count, poll, CPU masks, q8 KV, lazy PLE, n-gram drafts on prose, MTP at temp 0.7, and more than 2 cache uploads per step did not help. Cache size is ~100 MB per slot per GPU on Q6, and the user plans to test UD-Q4_K_XL next.