Personally, I would only go with a 3.0 in something 19' or smaller, and 19' may be a stretch if you want to do much towing, or get where you are going in a hurry. 4.3 is a nice motor, easy to find parts and maintain. And it won't work as hard to get you on plane and cruise. Lower RPM for cruise and you still have the get up n go, and decent top speed if you need it.