thats a trick question.
heres the deal. the coast guard cant tell you what you can or cant put on it. BUT, your state may have its own rules. that being said, if you put something on that is higher than the rating of the boat and you ever get into some type of accident on the water, your *** is in a sling. not to mention that the manufacturer and the BIA come up with those ratings for a reason. a larger motor is not only going to be more power but more weight to, and that weight has to be supported by the transom. if the transom cant take the extra stress, well i would hate to be you.
a 65 should move you along pretty good. if you want to go faster, get a bigger boat!
i hope i dont come off as preaching, just want you to know the facts.