I have a 750 on one side and an 1100 on the other. 750 fills up full and still leaves a lot of unused space around the hatch. 1100 never fills completely, but the rear hatch in my boat has every conceivable square inch of space filled. I'm guessing(again a big guess here) that the 1100 side has 150-200lbs more when both are filled up full. does your 750 fill the ENTIRE compartment front to back and from floor to touching the underside of the hatch?
I think this all depends on the boat, as each skiers model has a slightly different rear hatch setup and overall size...
'06 Supra Launch 20SSV-gone but never forgotten