As for the 68 and the 84, my average max speed from sessions on the 68 were about 27km/h, and my 84 is about 25km/h. That said of all the sessions I looked at on these wings, my single fastest speed on the 84cm was 31km/h vs. 29 on the 68. The 84 is all around more fun to swell ride, handles breaches better, and keeps flying in lulls. I had one session on the Moses that is similar to the 76cm and my top speed was 32km/h which felt way faster than the other two foils despite still being slow. I am no racer obviously, I just like riding swells and exploring upwind.

My experience is the H2 (Gamma) and I76 have a lot of overlap. Enough that if I was buying again I'd get the I84 instead.

My goals aren't speed though.