i'd say go a 7 should get you going in about 25. and a 10 would get you up in about 17 i guess. I'm 69 kg's. ride a 9m and 11m fuel and 129 lunacy. 11m gets me up in 17 and the 9 takes me to about 30.
Im 65kg ride a 125 board and have used my 11m instinct as a 1 kite quiver for 2 seasons, but gets hard above 25kn never had a time where it got to windy in the gong so i got a 7m this season to add to the quiver