RE: IS87 how similar is the ride to IS101
I use an isonic 87 with a 7.6m SSR and Drake 36 fin (off an isonic 111). I weigh 75 kg, and the combination is very fast and balanced on all points of sail, particularly in chop.
The 87 will take plenty of fin to provide lots of grip for big sails as the tail is quite wide. I have sailed the same sail on the sonic 95, isonic 105 and 111, so I can vouch that a 7.6 sail is effective on the 87. Of course better pumping and gybing technique is required compared to the larger boards.