Great report, for those who haven't sailed the iSonics yet. I am not a slalom racer, and I'd second your thoughts with regard to iS122 as a good cruising board. In steady 10-11 (or more) I have easily and comfortably covered some stupidly long distances on it. As for a top end, a few times I've survived hair-raising situations (for a non-pro, that is. 25+ knots in large chop, with a 7.3), that went far better than expected. As long as you have the nerve/balls to stay on the gas, it will steam through. And on top of it, you can really whip it round a gybe, something I wasn't expecting of such a wide square "plank". I'd like to add that my 122 (2008) definitely has less volume than quoted, you feel it when in zero knots with a big rig, but that's fine with me.
The only thing that puzzles me a bit in your report, is your 10 kts planing threshold with only a 7.5 (95 kg?). From my experience that's more like 8.5-9.0 sail conditions.