I'm 6'5" and 255 lbs and as you well know, everything is to small.
I have an America and I do find it small. Someone has mentioned the foot brackets; that might help some. I personally find the seat to be more of a problem (different seat on the speedmaster). It would be nice if I could move the seat back a couple of inches. As for switching to a different bike, don't know if it will help much. Thing are just not made for people 6 and half feet tall. I have been considering a Bonnie or a Scrambler because of the bench style seat. Although not designed so tall guys could stretch out the seat does allow for it.
As for power, no problems. I was on the highway with the wife on the back (under 400 lbs, and she would not appreciate me saying how much under

) and easily accelerated to 135 km/h (~80 mph) to pass.