Maybe you're right. I didn't consider the 122 as it's got almost the same volume as my Aero 127. On the other hand the iSonic 122 is probably a seriousely more aggressive board and it will even work with a 6.5 sail (even though my 6.5 is not a racer it's quite efficient, I've done + 30 knots with it on my ST 115).
The 8.5 will match the 122 quite well. Don't know if I wlll plane in 16-18 knots??