Best llama.cpp launch config for Qwen3.6 27B on RX 7800 XT (16 GB VRAM) for OpenClaw?

I’m trying to find the best llama-server launch command / runtime config for running Qwen3.6 27B GGUF with full GPU offload on ROCm. I’m currently using the IQ4_XS quant, but I’m not sure if that’s the best option for my setup. This is on Ubuntu, with the display connected to my iGPU, so the RX 7800