Well… A lot more fun than your Sea Ray.
But, No protection from the wind and waves. If it is a rough day you and everyone on the boat will get wet. It is basically an over-sized PCW that you get to take some friends along with you. My personal opinion is if you are coming from PWC to the Challenger 1800 you will love it but if you are coming from a family boat, it may not be to your liking.
MPG depends on how you drive it. Most of the time I'm Wide Open Throttle so it sucks gas. Your Sea Ray would suck gas if it was wide open all the time, just not as much as a two engine, two stroke, jet.