I'm trying to find what drive I want for my project boat. So what is the max hp you can put to a bravo 3?

I think it is the same as a Bravo 1 which is 500hp. Also take note that the Bravo 3 is intended for slower heavy boats. I don't think it is good for more than 70 mph.

well what I'm trying to do is on the crazy side, I'm converting twins to a single somewhere in the 650 to 700hp. now I do know that it will be slower. I'm building a sport-cruiser.
I was told I'll loose 5 mph toped out w/the 3 is there any truth to that?

Merc now offers a Bravo III XR. They put their 525's in front of it in Formula's big SS's. 5 MPH might be a bit high in what you will lose.