Re: How fast will it go?
ok, I didn't know it was rated for 40.........25hp on a boat that takes 40, my opinion, will feel underpowered. It'll plane, but not easily, and fall off plane too quickly. You'll have to cruise at WOT (the least fuel efficient throttle setting in planing mode) because backing off to 3/4 throttle (which would reduce fuel burn by half) will be displacement mode, even less efficient.
Understand, I'm speaking in general terms; I have no direct personal experience with this particular hull. I could be wrong.
I have seen a whole forum dedicated to Whalers, don't have the url handy, though.