My Oneida Osprey is set at 28-30lbs. I've taken some good sized carp in 4' of water with it. I've even gotten bigheads 6' deep... but that was shooting almost straight down.
My TNT Revolution is at 30-35lbs. Here's a picture of that bow and a good sized carp.
I may be getting a Mathews Craze to try out for bowfishing this year.