Do you have any fins beyond the stock fin (or did your board come without a fin (2010 iSonic boards do not))?
What sort of windspeeds and water conditions are you going to be sailing in/on?
What is your min. wind threshold (are you wanting to be the earliest 100 Kg.
planer in your area)?
At 100 Kg. you are possibly limiting your early planing threshold with a max. 9.5 m2
RSS race sail.
It would seem a 10.0-11.0 free race (V8 maybe?) would get you planing earlier if that's
what you are after.
As far as fin size, at your size, it would seem a 60-66 cm on a 93.5 cm would get you planing the earliest. (Maybe even up to a 70 cm???)
If you are after the best speed, 52-60 cm would be the range I would suggest, but I do not weigh 100 Kg. so I may not be the best guy to ask.
Fin selection is going to be dependent on whether you want the earliest planing, or the best speed..... two different goals, that each require a different sort of fin.
A big powerful fin/foil to get you planing early and keep you planing when the wind drops below your threshold.
A slimmer slippery smaller fin/foil that has the least drag to give you max. speed.
Hope this helps,