G'day Brian Big head sail is the way to go, Mitch Bayliss was here last weekend and he went like stink. I had a square top on my big rig Stingray though a lot smaller than the squares now. I found that to make the main hold it's shape I had to have tight main sheet but if I had the mast rotated properly it pulled the top of the mast over backwards and depowered the boat so I used less mast rotation. The 5.7's have gone from my square top to a F18 style, in light wind from what I've seen they seem to lay off quite a bit if you let any main tension off. Maybe super stiff top batten needed? Whats your new boat?
regards