Everyone's definition of usable is different, but I disagree with your estimation of the specs required to be useful. I am able to do useful coding on Qwen3.8-27b, with 100k context and 16gb VRAM, q8 cache. I feel I'm living right on the cusp... my GPU is old (2016, pascal), so to get usable speeds I have to drop to a Q2 quant - which still gets stuff done, but the difference with q4 is noticeable. Q3 is close enough I don't really notice the difference between it and Q4, but it's too slow on my system. More context would be nice, but it's not that hard to work within ~100k.