For pure freeriding on a Formula Experience board, I would pick right away a no-cam NCX 8.0 or 9.0 m2 sail. It's very light, it's very fast and still very much in control when overpowered. A 105 kg friend of mine is using both sizes on his Ultrasonic board with great fun and ease of use.
Since I weight 65 kg as you do, you will have no problem to start and sustain the planing as of 10 knots of wind with an 8.0 m2 sail and 8-9 knots with the 9.0 m2 sail. You will start the planing perhaps a tad earlier and point better upwind and downwind with a cambered sail like the Formula Experience OD 8.5 m2, but for pure freeriding without competing at a high level, you don't need that high degree of performance IMHO.
Hope you have a smaller fin to match your smaller sail in higher wind on such a wide board.