I have a 64lb bob lee signature td. It has killed a moose and a Dalls sheep and has since been retired. The moose almost managing complete pass through. The sheep was a spine shot, in which over 2/3rds the arrow passed directly through the center of the spine. (if you look at the bowhunting thread archieves on spine shots, most guys getting almost twice as much KE dont get the penetration I managed on that ram! The ones that do aint posting.)

They are a quiet smooth shooting bow. Mine is no speed demon by anyones standard but its no dog either. If ya find a good deal on one I wouldnt tell you to look else where for a bow.

I have however since gone to a checkmate crusader. 60lbs. It has also killed a moose and a sheep, not to mention a caribou and 2 whitetails.

So to answer your question is 55 enough, most definatly, if you do your part to set everything up right! not close but right on! The big thing is shooting a bow you can handle well. If its a 55 and you cant quite get comfortable shooting a 60, then so be it. For if you dont put the arrow in the kill to begin with, it dont matter how perfect, heavy, fast, etc your set up is!