Hi Eli, i had an IS 111 too but switched to a 101 due to my 70 kilos, what i learnt
from Isonics is that they like cambered sails the most, with a cambered sail you get on plane sooner as cambers get you going forward more easy so you don't have to force the board too much downwind. In four/five sessions you'll get dialed with it. Well done downgrading the fin. Just my 2 cts.