Stumbled across this and thought it had some really relevant info. I've noticed some of the boards that I've ridden with rounded rails seem to ride smoother and stay upwind better than those with really hard, sharp edges

yeeees...
...i've noticed that my tits are bigger than those of that nervous guy in the white boardshorts ....

anyways...

as of the windsurf board's rails are sharp only at the back where the water is released from board surface, and it is smooth where water enters under the board. so it is logical to use same theory on the kiteboards.
only thing, if you use the TT you have tail and nose in one! so, you have to compromise.

probably sharper edges on both tips will increase speed but reduce manuverability. and a contrary rounder edges slow speed a bit and make a upwind and turns easier. i guess it is best to have sharp edges in the middle of TT and round shape on the tips, but thats the every rider to decide for him(her)self.

winds