How Much HP Can a 8 3/4 Handle?

I think you should consider a 904 instead of the 727, I use one behind 600 HP without problems. I also use an 8.75 rear with the MP aluminum center section, better than any of the cast iron ones. I also use a pro gear which is only available in one ratio that I've found, 4.88.

It holds up with a foot brake or transbrake but a 4 speed would do it in. If I had it to do all over I would have built a Dana 60 though. Much cheaper in the long run.