I ride behind the 2008 C4 Avy a lot. It came with the center tank which doesn't do much at all. Wakeboarding:
Center tank full, 400lbs. in the Port locker, 350lbs. in the Starboard locker and 750lbs. in the bow.
Carter is right about the speed. I find that riding between 24 and 26 cleans up the wake. I have never had the wake be perfect on both sides but as long as it is hard I don't mind much. Wakesurfing:
750lbs. in the locker, 400lbs. on the seat and 400lbs. in the bow with the center tank full as well.