I think Devon wants to avoid breaking the mast, I found the mast tuning is unbelievably critical, I was keeping up with Fergs with my small head main, even beat him in our distance race when he had the new Goodall Bighead with new mast supposedly tuned for the sail, he lessened his prebend by 30mm and softened the diamond wires a couple of weeks ago and smoked me. I havn't heard of a Nacra dealer doing different sail design, I thought it was all class stuff, did he say he's done it for other I17's. Sorry Sam my bad,I don't want to hijack the thread but to save my already ragged reputation, I'll give one last link to me sailing in a blow when another 5.7 pitchpoled, it shows me and my wife mucking around keeping the boat flat.
http://www.youtube.com/watch?v=SmzwEhc_83w
or
http://beachcatsaustralia.ning.com/video/sailing-10410rain-and-30kt