Think about the Carve 121 then.
Yes, 2 sails (about 1 m2 apart) would be much better.
A 6.5 will not get your going on these boards in < about 14-15 knots.
A 7.5 will get you planing in about 12 knots, but will be too much sail
(hard on the arms) @ 16-17 knots.