my home spot is a lake, windconditions there are usually between 10-20 knots and most of us sail 135-150 L boards (the light guys take 120). I have no idea what the compact is and i couldn't go for the Ftype seeing as you said you didn't want a formula. but as a freeride the futura 122, i think, will fill your gap (40+L of floating volume should do the trick). The IS is a great idea if you really want to and it might even be better for your gap seeing as it carries larger sails. but like you say, thats an expensive move to make (you could always look for second hand IS, loads of slalom guys use their IS only one year, sell and buy new stuff).
hope this helps
Haiko, AKA crazychemical