Qwen3.8 27B at UD-IQ3_XXS Fits Over 200k Context in 16GB VRAM, at the Cost of Half the Prompt Processing Speed

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A r/LocalLLaMA user moved from UD-Q3_K_XL at 140k context to UD-IQ3_XXS and cleared 200k context on a 16GB eGPU (Aorus 5060 Ti AI Box over Thunderbolt 4), with KV cache quantized to q5_1 and llama.cpp built with DGGML_CUDA_FA_ALL_QUANTS=ON, served without MTP or mmproj. The tradeoff is prompt processing falling from 700-800 tok/s to 400 tok/s. A commenter running the same model on an RTX 5080 with KV at Q4_0 and vision forced to CPU via --no-mmproj-offload reported 1750 PP/s and 85 TG/s at 132k context, which is the better-balanced configuration of the two.