Most boats have a HP limit. For a good reason! As long as you dont exceed the rating, the more the better up to the limit. With that said, i'd use the most reliable vs the most power. A 4.5 is not much help, and drives more like a pontoon than a boat. I'll bet I know places you could'nt outrun the tide with a 4.5. It might be great as a kicker or backup, but only if you have the wieght to spare. And something with a rectifier to run those lights!

Good info above!