Thanks for the good answers, I've definitely got a lot of good response
My hope was to find a board-sail combo which peaks in winds between 11 -15 knots. And I wonder if an Ultrasonic with a 9m can do the job perfectly, it sounds like.
But a Isonic137 with a 9m also sounds interresting.
Thanks again for the good answers.
Ps. Have you heard of the formula which says that sailing max. speed of the board are: wind speed x 1.5? So it on a previous thread