I wish each quant was benchmarked on the same tests as the original network so we could compare their performance
When I tested various eval benchmarks on Qwen3.5/3.6 27B with Unsloth's quants, the scores usually dropped 0-5% between UD-Q6 and UD-Q3 depending on the eval.
Unsloth publishes KL divergence numbers which measures how much the quantised probability distribution changes vs unquantised: https://unsloth.ai/docs/models/qwen3.8#quantization-analysis
It's a bit bare at the moment, I assume they are going to add further detail later (eg comparison to other quants), similar to their other releases.