I spent a fair amount of time on the 115 when it first came out 2 years ago and I'm about 85kg. I sailed the board in windy vietnam with 2 race sails, neutron 6.3 and 7.6. The fins used were the stock drake 32, vector canefire 34 and a select elite 36h. The board will easily take the 7.3.
Its a superb board, perhaps one of the best allrounders I've ever sailed in that size. You may lose out a little to the dedicated slalom boards in the straights but in the turns the stype shines and shines. There are boards and moments on them that stick in your mind; for me one such moment was the second ever gybe i did on the S-type. Coming in between swells at Mui Ne bay vietnam, the board went through the gybe in a silky controlled way that I can still clearly remember. The 126 felt completely different, more bulk of course, but also it was not as communicative or as lively as the 115. I would stick to the 115, my use of it was with sails ranging from 5.x to 7.x.
As an aside on those 2 10 day very windy trips the other boards I used were the Sonic 100, Thommen RS60, Kombat and the Stype in 2 sizes with the Stype 115 being my preferred choice for sheer sailing pleasure.
As for fins I did a write up of my test findings on our site and if you are interested you might want to read it at this link : S-Type - 3 fins and a board
hope this helps..