RE: q on isonic and sails
I haven't sailed iS87, but I can offer you my experience wrt to sail carrying range. I was in situations when I wanted to extend a board's range to the max, and beyond (as you say). I believe that there is a limit to which you can push this, and after that you don't really gain anything. Example: iS122 quoted range is 6.0 - 9.5 sails. My findings (and other sailors' too) are that I would never use it below 7.0/7.3 or above 9.0, unless I was very heavy, very light, or for easy freeriding (not powered slalom blasting).
On top of this, I don't think that going to a 5.1 would be justified (about 9% to your next sail). Above 27 knots (force 7), the water state will play a significant role.