Something else to think about - Formula boards are designed to go up and down wind, they're not very happy just beam reaching across the wind, the massive fins tend to try to lift the board out of the water for a start.
Personally I don't like them and unless you're racing or really want to plane in the lightest possible wind (which means you need a 10-12 m2 sail and new mast and boom) You'd probably be better off with something else - big (120-140l) freeride or slalom if you feel the need for speed

and 7.5 to 8.5 m2 sail