r/LocalLLaMA 'Q4, Q5, Q8... why?' - community opinion on where the quantization quality cliff is, plus one user's own 3060 A/B test

OP u/mrmojoer (newbie, M2 MacBook Air). Named participants: timschwartz, Ars-Paradox, Randommaggy, mrmojoer. Prominent claims, each a single opinion: timschwartz 'Stuff below Q4 is usually too smooth-brained to be useful'; Randommaggy 'For coding anything below Q8 is beyond useless unless it can plagiarize an answer wholesale'. The ONE measured element: mrmojoer ran llama2-7b/13b-chat-q6_k, mistral-7b-instruct-q6_k and mistral-7b-instruct-q8_0 on a 3060 12GB, prompting for 53 'wh'-words in alphabetical order; llama2 gave 25 words and lost both constraints after the first few, mistral gave 53 but lost them after ~15-17, across multiple sessions. That is a 4-model x 1-task n=1 result and is NOT evidence about Q4 vs Q8 - all four models were Q6_K or Q8_0. Recorded for the opinion, not the benchmark. 2026-10-11: Automated access blocked by Reddit (HTTP 403). Community thread on quant quality floor preserved as forum opinion record; confidence unchanged at 0.5.