No the 657X is an edgy little engine as it is. If you stuck a 720 in it then you would only get a 5hp gain and that's the last engine in the series(made till 05 I think). I'd keep it reliable and put it up for sale while you enjoy it. Look out or a 95-96XP or 97-99SPX and you will get 110hp(you have 80 now) in a similar sized hull that handles better with reliability and more resale potential.