ORIGINAL: tbyrd
I think at 55lbs you could still shoot a mech. broadhead. You could drop down to a 75 grain tip, which will give you a little more speedand shoot the RocketMiniblaster, which as a 1 3/4 in cut diameter, an awesome broadhead. But if you want to stick with 100 grain tip try the Rocket Hammerhead, it has 2in cut diameter and I bet they will still open with the poundage you shoot. I have used both of these mech. broadheads and they are awesome.
With all due respect a 2" diameter cut out of a 55 pound bow is a recipe for a wounded deer. He needs a conservative diameter mechanical (1 1/4" max) or a cut on contact fixed blade like magnus stingers.