My neighbor is about to mount two Yamaha 300's on the back of an 23' cat hull he picked up this winter. He has the Stage 3 mod kits in both and according to the company that puts out these kits they should be putting out about 345 each. Not bad.
Down here in swamp country it's always a race for who has the fastest bass boat. Several friends have Bullets, Gamblers, Allison's, etc. A guy down the street from me has a 21' Gambler with a Merc 225 with the hi-po lower unit and a few mods and I've seen his boat out on the water many times. His GPS has recorded high 80's to low 90's. A 100 mph bass boat is not out of the question. Ex-father in law had an 18 1/2 Sprint with a 175 Yamaha and I was in it when we hit 70 gps and still had a little left in her.