RE: Max sail size for a board
In reality, I think minimum and maximum sail sizing for boards is a bit subjective because there are quite a few factors which affect performance, and some also have an awful lot to do with the sailor's size and abilities. One important thing to remember is that a board's rockerline can make a lot of difference, which I'm sure gives the iS111, with its flatter more speed oriented rocker, an ability to use larger sails successfully. It's my thought that the curver rockers of the Carve and Aero find it tougher to benefit, especially since they are more focused on maneuverability rather than raw speed and accleration. Also, big sails aren't known for there quick maneuverable handling.
It is interesting to note that Dolf Daam has been using a 9.0 Hot Sails Maui Superfreak with his Aero 117, but he went with a larger than standard custom fin to better balance the sail's area. He has been very vocal about his happiness with the combination. But, considering the recommended sizing, the situation is clearly outside the viable margins.
Generally though, I find that the width of a board (at the middle and tail) indicates a lot about the size of fins it can used, and the fin has direct bearing on sail sizing possible. Still, volume and its distribution enters the picture too, because if the wind drops to questionable levels the board must float everything in a balanced way.