RE: isonic from 10 konts
From your first email, seemed you wanted to add the new board to your quiver (C121+ K96), so considering that and the 10 kts lower wind range -even the discussion of unaaceptable FW option - (together with 16kts specified max), the choice would be for a bigger iS (122/133) to take advantage of fully covering the lightwind range very effectively, then switch to C121 as wind increases.
But... If you want to take one iS to replace C121 and also cover the wind range down to (around..) 10 kts, then yes, the iS115 and iS111 (07) is also good to consider, but please be aware the light wind range 10-12/13 kts will be more compromised, but the top end range (of course ) much much better. The 2-3 kts between 10 and 12 are really critical in terms of ideal equipment size choice etc, those 2-3 knots matter a lot compared to (say) 20-22 kts.
As always, if you are uncertain, please try and arange a demo or test ride of either the exact board, or even a similar one in the family to give a benchmark in your exact situation.
Hope this helps resolve the choice, of course, let us know if you would like more info or discussion.
Cheers ~ Ian