mcross,
I've successfully used a 44 F-Hot carbon in the iS110 with my 8.6 and a 40cm C3 StingII with the 7.8 and 7.0 (Loft Racing Blades). In the iS117 I just use the 44F-hot for both 8.6/7.8 combos.
Twin cam versus triple cam versus four cam sails - most sailors say there is very little difference performance wise between 3cam sails (e.g Severne Overdrive, Loft Switchblade, KA koncepts etc) and respectively their full blown racing sails (e.g. Reflex, Racing Blade, KA Race). Twin cam in big sizes similar to say an Ezzy Lion (I think) would be just as good in lighter winds but potentially the 3rd cam offers that little more stability in higher winds (and through lulls) and then when you get ballistic winds (say +30kn) speed sailors tend to get a full on race sail (<6.0m) with 4 cams for maximum foil stability. One major benefit with the 3 cam or two cam is smaller luff sleeve eliminating difficulty in water starting / uphauling if luff fills with water.
here's a great thread on the Overdrives too
www.seabreeze.com.au/forums/Windsurfing/Review/2014-Severne-Overdrive-R5/