I bought a I-sonic 122 2008 model, end of last year. I bought a GT31 at X-mass.
I have only recorded my last 11 sailing session so far. In winds form 6 to 18 knot gust I have recorded just over 26 knots Max Speeds plus Max 10s Avs just over 25 knots. Using a 7.5 VGM & Arrows TForce 6.8 using a Select Weed Eliminator Fin.
Because there is not much and the water stays flat and when the gust hits you of around 15 to 18 Knots you get a good speed run.
In winds of about 15 Knots Max I'm doing around 22Knots with my 7.5 VGM.
When I get a bigger sail for the board I will be able to do over 20 knots in winds around 12 knots may-be.
Sea Breeze should have a section where you can register your GPS speeds for all makes of Boards!!