What will be effect of using too big sail for the specific board?
My favorite at this moment is JP Slalom 118L and the biggest sail was so far North 8.0 RAM.
Combination works perfect for me but the best wind condition are between 20- 25 ktn.

I am tempted to use bigger sail below 20 ktn ( 15 -20 ktn) . What could be the biggest size I could utilize with this board?

I bough recently and tested old Gaastra 9.8 Nitro with my 130L in very light winds, But this old board Fanatic X-ray is not really for speed.

I am tempted to use this Gaastra 9.8 with JP Slalom 118L .

What will be first sign that this set doesn't work ( assuming that I equip the board with bigger fin now from my 37.5 Black project)
What fin size should I use for this combination ?