RE: Different technique required for isonic 101 for speed compared to traditional shapes?
Ned_321, Ronny is right, 35 is much too big on a 6.2 for speed. I have sailed my 06 105 with a 6.6 TR-1 using a 28 cm Tectonics Goldwing fin, with very few spinouts, and I am not such a good sailor. You can surely go much smaller than 35 on your 6.2.
Anyway, I do not think that all-out downwind speed is these boards' strong point, it is rather their speed on all points of sail, especially upwind and on a beam reach, and ease of use.
Let us know your speed after you've dropped fin size.