Thanks Gesty, one other reason I chose this fin size is that most fin manufacturers I researched, after I used Adam's fin, recommended it with my two main sails (6.4 & 7.5) with the 6.4 being the more recommended one which you suggested too. Which is fine as I intend to use that sail and probably a 5.8 in the near future with that fin too.
I really feel a 28 will be too small with a board of this width in 15+knots. In a previous life my f'glass waveboard often spunout with a 25cm fin, and the tail width 1ft from the tail is exactly 100mm difference to my current board (both board's rails shapes nearly the same). So with the wider tail it's got a pretty good chance of spinning out too I reckon. But fin shapes/profiles have changed a lot since then. I'll see how it goes with the 32, it's in transit now.
Adam, yeah I thought it would be a case of "suck it and see" too. BTW check your fin again, it did say "Free
wave 33" somewhere on it, I'm sure of it! If I'm wrong I owe you a beer.

It's more wavy shape than my 42 Freeride too which is more upright.
Wind for Wednesday is looking promising but ocean is still brown, messy and scary looking. Might get to use the GT-31 for the first time in the lake but it's forecast for a southerly...

, that big arse mountain always get's in the way in that wind direction!