I shoot a High Country bow that has been shortened to my 26" length. Even with the bow cranked up, I can only shoot 63 pounds. I have been shooting 315 grain arrows(with broadheads) with no problem and no real noticeable increase in noise or vibrations. Of course, I have all of the goodies on it. I shoot about 273 fps.

I saw an ad the other day for super-light carbon arrows in the 235 grain range that were meant to be shot from 70 pound bows.
That should increase arrow speed a bunch.

Good luck!