Rumour over here (we have a guy at our club that experiments alot with these things) is that slightly inward angled boards reduce the pitching up the boat. The boat sails calmer in chop and such and this will lead to preformance gain. The lift of the boards seem to be way to small matter in a significant way through reducing wetted surface.

But like I said it is just a rumour at this time. He also says that he sail 5 to 10 degrees higher with them but I didn't see that happen.

Wouter