Bryan,
I am glad to hear that Fantail performs well to windward in a blow, but I am not surprised, really. Fantail has a good hull with plenty of keel, ballast and rudder, so will take care of you. Fantail also has a fairly short, light and slim mast (compared to all-wooden masts), which definitely is an advantage here. I also found that even my first, perfectly flat sail (on Malena in 1990) worked quite well in a blow. The big advantage of the JR, apart from saving us from working on a jumping deck, is that it is easy to set the right sail area for the conditions. Camber and pretty setting of the sail seems to matter less in such conditions. Remember, in strong winds, the apparent wind is closer to the true wind, so we can point surprisingly well on the compass or GPS.
The reason why I make a bit camber in my top panels, is not only to cope with light winds. I find that the little bit of bagginess ensures that the reinforced leech stands taut, and never ever flutters. I think avoiding fluttering is important to make the sail last.
Arne