I'd have to do the GT300 if it came down to deciding on the 2. They'd burn me at the stake if I missed that race.
I did my first GT300 on a 21se and have to say it was the most comfortable ride in a distance race ever. Keep that boat. I regret getting rid of mine every day. You're right about the wings. They keep you pretty dry and comfy. I'm making some "Aussie 18" wings for my N20 just for the extreme adventure trips. At our Team Chums website, you can see some photos of the GT300 in 2004 when I did it on a 21se. You've peaked my curiosity quite a bit with the idea of this race/adventure. Why don't you go after a sponsor for the event through a media buyer and get it sponsored? Or even find a production company to film it and sell it to Nat Geo or History Channell or one of those channells. Just a thought.
BTW, the name plays well. Keep it tagged to the event.