RE: iSonic 87, 94 or 101
It's an each way bet, and either way is a winner.
iS87 to iS101 is a healthy but still practical overlap, 101 will allow a very good range in powered 6.7 conditions (in which you could be on either 101 or 87) but obviously less bottom end.
With 111 you still have reasonable (small) overlap, most likely you would change off 111 at "medium" 6.7 conditions onto the 87, but with 111 you pick up more bottom end range. In my opinion, it's not so much that the 111 has a lot more early planing potential, rather it can comfortably carry enough extra sail to make noteable light end difference.
In a pure technical sense, the iS111 sweetspot is going to be centred around 7.7m (and still give the chance to sneak a 9.0 m on there in really light slalom if you can be bothered..), whereas the iS101 sweetspots more a round the 6.7m, it's still fully capable with 7.7m but no way on the 9.0 for regular style sailing.
With 75 Kg, it probably gives a little extra advantage to choosing the iS101 in terms of early planing c/w sail size etc, also if you tend to be a more active or aggresive rider who prefers a slightly "smaller" board (work a bit more to get it / keep it going, but enjoy that extra efficency when you're fully lit).
I think we're probably slanted in favor of the 101 as it really is a standout board - (time will prove that) - plus we got the full back up of the 122 when it's really light slalom. If we had only one board to choose, well....
Cheers ~ Ian