I am looking to purchase a new Sun Tracker 18' Party Barge...Max Hp for the boat is 75HP, however they also have a merc 60hp Big foot....Is the 60HP Big Foot equal to a straight 75Hp? or is it worth the money to upgrade to a 75? Also, outside of warranty loss, can a bigger engine be put on this boat, like a 90 or a 100Hp...Thanks for the help!!!!