Thanks guys for the email to Vector Fins, I am not sure that was the one I found on their website, but I wrote Jeff once more and hopefully I'll get a reply this time.
I will be looking at getting 2 fins (hopefully CaneFire fins are available!) sizes 38/40, 40/42 or 38/42; I am guessing that 38/42 would provide the greatest flexibility in sail size.
I've been wondering about this. My 07 Isonic came with two fins, a 36cm and a 42cm, but it seems as if most people tend to use the larger fins in general. I've had some success with my 36cm in slightly overpowered situations, but should I just stick to the larger sizes and ajust the mast-foot acordingly to compensate the extra lift ?