fins for isonic 50
I was wondering if anyone could recommend speed fin style and sizes for isonic 50. I use 2008 5.8m ka koncept and have done 40 knots on both the std 28cm slalom pro drake fin and 23cm drake speed fin. I have a 21cm tectonics on offer at the moment and also don't mind the sl7 select fins but don't know whether to go for a 25cm or 27cm or go for a smaller speed fin - 21cm tectonics or 23cm mal wright fin???
Any advice would be appreciated.
(1.75m tall and 77kg's)