Re: 2000 mercruiser 350 mpi modifications
You DO NOT need an engine change. That boat should perform MUCH better than it is with its current engine.
Try getting some of the gear out of the bow. I know that shouldn't help holeshot, but it might be keeping your bow in the water at WOT. 3 batteries, a full water tank, and a full hot water heater is "a lot" of weight in the stern. But again, nothing that can't be overcome.
You keep mentioning "knots" as you speed measurement. Do GPS units really measure speed in "knots" or is it really MPH?
The reason I say the boat doesn't need a engine is that my father had a Chaparral Signature 27 cruiser that was 9' wide, and definately weighed more than your boat. It had all the same things you mentioned, water system, hot water heater, 3 batteries, and a 350MAG MPI with a Bravo 3. I don't remember his gear ratio, but he ran a 22p propset, and he was very happy with holeshot and top end speed. He got 42mph at 4800rpm WOT in his. And got about 2.2 mpg at cruise. Yes he did have to run 3500rpm to get a nice cruising speed. I spent lots of time on the boat, and while it was not holeshot rocket, it never felt labored. Even LOADED up with the gear that we three people took on a 9 day cruise once.