i-sonic 122 or 133

hi

i have been looking for a second hand i-sonic.
i am surfing at a light wind that cahnges between 12 and 18 knots. i am using a 7.6 gaastra nitro5 race sail. i have found a 2007 133 isonic but people say that the board flies when there is high wind and a big sail so dont buy more than 122 lt. and i am going to buy a new sail at 8.3 sail m2 or more and i am 74 kg. so what is your offer