Are you referring to the HCl or the Freebase? With the HCl it's much more common to see doses over 100mg as it is quite a bit less potent. With the freebase even 50mg is quite a strong trip - I feel like anything over 75mg or so would be too uncomfortable physically for a lot of people, and the visuals would get rather distracting as my experience with 50mg was
extremely visual.
For people who aren't overwhelmed by bodyload on the come up etc with aMT I could see the 75-125mg dose range being interesting if they're looking for more of the traditional tryptamine mindfuck and profundity rather than the more easy-going experience that aMT usually is. Anything more than that seems like it would be excess and unnecessary. I can't speak for dangers, but I imagine at higher dose ranges like that the serotonin release would be significant enough that you should at least apply a similar "one month" (or longer) break between trips in order to avoid serotonin downregulation, as with MDxx and x-APB.
A little search revealed
this trip report, where someone took 200mg - he seemed to have quite a bad experience at that dose as his left him rather worse for wear several days after. Sounds like he might have had an episode of depersonalisation/derealisation, or it could be a similar hangover to MDxx, but hard to tell.