In my experience a Formula with a 10 m2 sail is not planing particularly early for a heavier guy. Not much (or any) earlier than a big slalom. The Formula planing advantage becomes obvious when taking a bigger sail, in the 11.5 range. Then there is a significant difference in planing threshold!
But I agree that you should be able to point much higher with a Formula, even if the planing threshold is the same.