I have an '06 LSV.. I have running the stock 400 in center locker about about 400 in each rear locker (I have 750 lb sacs but don't fill them completely). The LSV Hull likes a little extra weight in the bow..
What speed do you ride? How long rope?
I ride at 21ish and 70' and am very pleased with my wake with approx 1200 lbs ballast..
Your '07 should have 400 in center locker and 400's in each rear locker.. ('06's came with 275's in rear..'07 switched to 400)
fill the center sac full (make sure it does not have too much air in it.. sometimes this one can fill with air and not get much water in it!) and start riding at your normal tow speed.. monitor the wake as you fill the rear sacs. you should have a nice clean wake above 20 mph with just the center bag full.
Also, do you have a wakeplate? if so.. how do you set it?>
lots of variables here.