With time on the board to get comfortable, you should be able to handle at least 20 knots in flat water. You may be able to go over 20, but you will probably need a smaller fin and smaller sail. In 20 knots in open or slightly protected water with 1/2+ meter chop, the ride will be a little crazy with the 6.6.
For you, I think the board is best suited for a 7.2 sail in about 11-14 knots. 6.6 sail in 12-18 knots and a 5.8 sail in 18-22 knots.
I haven't sailed this board, so these are just estimates. Hopefully someone your size with an F111 will jump in and provide a better estimate.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.