RE: isonic 122 and 9m which fin
If you're sailing overpowered on 9m/120kg/iS122 then the fin loads are going to be rather hi. For optimum performance in this mode you should try fins with less flex than normal, sizes 46-48 will be OK for medium powered 9m or something 42-44 for more fully/overpowered especailly if your board speed is high (flatter water)
Stock fins are fine for average use, but realistically these are optimised for typical rider loadings, which delivers better more accesible "mid load" performance.
Cheers ~ Ian