I use the JP Australia Freewave 93 when the winds, but mostly the chop, get too much for my Fanatic Blast 100.
I have the stock freewave fin, 27 CM, what should I use on it for more speed and faster planing?
Sailing on Texas Lakes, but I sailed in Melbourne once!
Gary
If you cannot tell us your sail sizes, then your option is to look at the JP specs ...
example ..
jp-australia.com/p/windsurfing/fins/freestyle-wave-fin/