Pre-bend will flatten the sail, but will also increase twist. Just pick a quiet day, sheet in the main and begin adjusting the pre-bend. Take out pre-bend and the leech will stand up, increase pre-bend and the leech will open so you need more mainsheet to control it. Putting the boat on its side and playing around with pre-bend, mast rotation, downhaul and sheet can be really useful. Lots of stuff to learn from that.

A stiffer batten will probably flatten the top, which is not what you want in light winds? Getting the mast and sail tuned right is a major performance issue <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

I think a closed leech can be fast in certain conditions.