You have the Futura 101 (that is a awsome board, and great choice for speed sailing off the wind,,), and the 95 Isonic will be to close to this, and 85 / or 87 will overlapp easily to the 101 Futura.
Form your information of how much you will use the board. I would reccomend you to get the sonic 85. The money you save, you could put towards a board in the bigger range (125+) - in the future. (as I guess this is the boards you will use mostly in your conditions?)
The difference between the 85 and new 87 for GPS sailing / free sailing is very small. If you do full on slalom competition, for sure the 87 would have a little edge on the 85.