Well, I don't know if I could apply the all the math from some of the recent threads on RM, HM, etc., but I did have a chance to take a proa on her maiden voyage today (see photo in attachment). The word I heard most from curious onlookers was "interesting".

20 feet long, 14 foot beam, 200 sq ft of sail, and a rudder at either end. You don't tack a proa, but rather you "shunt" them (steer to a reaching heading, release the sheets so that both masts pivot to leeward, pull one rudder, drop the other, sheet in the opposite set of blocks, and go. It was rather strange in that no matter what point of sail we were on, the view is always to leeward.