Steve,
That sweet spot range in the lower teens. Upwind (with board down!) it helps a lot. Above 15 a reef is well suggested. And we use it downwind without the main on lazy sails back up from Hadley.
Boy, do my hands hurt from hauling the halyard yesterday afternoon! Lots of McLube a great help. (On the foil and luff tape, not my hands.)
Ah, images up to 200K! Yay!