I just read this thread right through, and it started off such a serious topic!
So annoying when all you want is one piece of information and things digress onto other subjects and end up in arguments! (adds a bit of life to forums though I suppose) lol
Personally I think as long as you're not insured anyway, whatever damage you do with a slightly over-rated engine you would face the same problems uninsured with the 'right sized' engine for the boat. so stick the bigger one on as long as you're sensible with it! - remember it all comes down to the person on the throttle that is in control at the end of the day!