I guess I will add my .02 to this prebend square top stuff. I had Smyth build a sqaure top mylar/taffeta for my 5.2 and told him to design in some prebend. Once I got the sail I swept the spreaders and prebent the mast to match the sail. With the addition of some new downhaul, I was quite pleased with the outcome. It is another of those you get what you pay for things.

As to what sailmaker to use, make sure that they routinely make multihull sails. The usual mono suspects are not used to seeing the apparent wind that far forward, and I suspect you will not be pleased with the results (especially if that involves recutting a brand new sail to get it right).