5.6, 6.3 and 7.0 should go nicely on the 90. I haven't tried anything bigger than 7.0 so not too sure how the 7.5m would go; might be on the big side for this board. Remi, have you tried bigger than 7.0 on the 90???
As for fins ... I'm using a 32cm SL2/SL4 (Deboichet) most of the time in this board as that seems to be the right size fin for the tail size, regardless of the sail you have on it. I think your 34 Talon would be nice on everything for 5.6 to 7.0 actually but if you want a bit more low end grunt with the 7.0 then a 36 Vector could be nice as they are a little less powerful than the Deb 36cm which is probably a bit big for this board. A 32cm would be better if you are taking it out in really strong winds!
I run my straps in the front holes (front and back straps) as I'm mostly using this board for psycho-nuking conditions (ala +35 knots) which allows me to keep the track in the middle of the board which seems to be the best place for most conditions and not have the nose fly around too much. If you are just using the board in regular 15-25 knots maybe try the straps a little further back than the front depending on how tall you are and your weight.
The 90 is nice... hope you like it ;-)
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