I pick up this thread. My experience:
1) iSonic 127 works well with 9.2 sail and 51 Select S 10 51 cm fin. F-Hot 52 cm is about the same but it wibrates over 20 knots speed. The speed is ok.
2) The board works well with 8.4 and 7.6 sail with Slect S 10 46 and F-Hot 46 (also wibrates) but I think the board could go faster.
It seams like the fins over 50 cm is a bit faster than the 46 cm and I do not know why it seams almost impossible to run the board over 25 knots speed in chop. I think my scills are ok and I have ok racing TR-sails: 7.6, 8.4 and 9.2.
Please help me to go faster! I sail at sea but not at open sea. There are islands all around my home spot. Should I try other fins or what?