need more power

[Shrek]

I can't leave anything alone. Now that I know that my cc will do 44 knots with a full tank and two guys plus bait, beer, and fishing gear ... that does not feel fast enough. What are the potential drawbacks to putting something bigger than my 225 on the back.

like this
http://neworleans.craigslist.org/boa/2348085900.html

I'm not trying to reinvent the wheel here, and I don't want to try to turn this old off-white girl into something that she is not. That said, the weight of a 300 two-smoke is comparable to my 225. What kind of transom mods are we talking to make this happen and what kind of performance do you think I'm likely to see from a 75 hp increase?

Opinions gents?