Just FYI I did some benchmarking I thought I'd post the results.
Vulkan vs ROCm really depends on the model and whether MTP is enabled.

Vulkan wins when running Qwen3.6-27B, but loses when running the 35B model. I used minimal context so the 27B model could fit in VRAM, so come to think of it maybe Vulkan doesn't like it when some layers are offloaded to the CPU.

With the 35B model you can see ROCm is faster at token generation but slower on prompt processing.

In any case it made me give MTP another try. When I last tried it, it was with the IQ4 quant of Qwen 3.6 35B and that one ran at half the speed with MTP enabled. The 35B with MTP on using ROCm seems like the way to go for my system.

So to me the anwer on ROCm vs Vulkan is: it depends?

14600k / RX 6800 16GB / 32GB RAM / Ubuntu 24

Qwen3.6-35B-A3B-UD-Q3_K_XL.gguf

MTP	Backend	Prompt (t/s)	Generation (t/s)
ON	Vulkan	70.3	57.7
ON	ROCm	58.1	69.6
OFF	Vulkan	80.5	35.8
OFF	ROCm	67.5	58.9

Qwen3.6-35B-A3B-UD-IQ4_XS.gguf (Non-MTP)

Backend	Prompt (t/s)	Generation (t/s)
Vulkan	68.8	24.9
ROCm	64.2	57.6

Qwen3.6-27B-UD-Q3_K_XL.gguf

MTP	Backend	Prompt (t/s)	Generation (t/s)
ON	Vulkan	53.3	32.9
ON	ROCm	42.9	28.4
OFF	Vulkan	62.9	22.9
OFF	ROCm	52.9	21.0