Which boat? Deadrise? Underpowered with 140's?? Is it top speed or mid range performance/bar work that is most important? With twins of same hp as single, you lose out on top end, but mid range/bar work performance is so much better, with probably same or possibly even better economy (at cruise) if set up right. Personally I wouldn't have thought 140's would be too small (they are a great engine), would even be considering less hp. Don't like heavy ar$ed boats. 40kn top end plenty enough in my mind, well my 2c anyway
Cheers
Brendon