I sail my122 with a 8.5 as biggest. It can take more, but I'm 95 kgs and the board is actually only around 114 litres so with a heavier rig it becomes a sinker and I may as well go for my formula. I use a 46 fin for my 8.5 when blasting and a 40 fin for maxed speed even with 8.5. Anyway the board points highest when I am max powered with 7.0 and 40 fin. An iSonic needs power and speed to really work.
I'm also considering the 101, but I think it will sink too much for me. At my local spot the wind can drop quite fast and I doubt the 101 will carry me home in 4 knots of wind.
Do you measure your speed with GPS. I've been on +30 knots on mine, but actually that's not more than I did on my S-type 115 or carve 111/145. I don't think the 122 is faster on max speed than other boards, but its average speed, pointing and especially acceleration is excellent.