How bad is the gas consumption?

Looking at a 2008 Wakesetter 247 xti as well as considering the 2014 Moomba mondo. How bad will the gas mileage be on these? The wakesetter has a 6.2l Hammerhead 383, and the mondo would have a 5.7l 330hp indmar. I am used to a 3.0l mercruser 135hp....I am counting for a huge difference in gas consumption and have already planned for that, but I just want to know specifically how much of a difference it would be. About how many hours will it be of wakesurfing and wakeboarding before having to fill up?