RE: max sail size Isonic 111.
The main difference comes from the planing area /tail width (tail area) which allows the iS111 to carry more sail (and importantly big/ger fins, to allow efficient match to the larger sails).
In fact, SX(m) @68cm wide is rated at 8.5m sail max by F2, so a 9m rating on the iS111 is not that much different in reality.
iSonic design allows use of a high/er aspect ratio (more efficent) planing surface area at the back, while the control, comfort and jibe etc remain really first class (something that normally gets compromised with a wider board or wider tail area).
Hope this answers the question, please let us know if you need more info etc.
Cheers ~ Ian