My sweet spot with an older succinate batch was 125mg, which should be ~63% 6-APB & ~12% 5-APB according to my lab-result (it was quantified as the HCl salt though, so I had to adjust the molar masses and convert them accordingly).
A friend of mine took 150mg of that batch and was floored, never seen somebody gurn that hard. Real good entactogen imo, but like you said, very heavy, long-lasting, and quite visual too. Felt pretty drained and physically exhausted the next day but had no mental hangover or dip whatsoever, which was nice. I‘d say it‘s my second favorite entactogen, only surpassed by 4-FA.