Sorry Jake I think your wrong.
whilst the reynolds numbers might be similar for dagger boards and high speed aircraft, I haven't checked, you've got to remember that the rules change when you have to start considering compressibility and shock waves.

theres no reason why a symmetrical foil should produce less drag at the same lift coefficient as an asymmetric one, I suspect it would be the opposite.

I don't see you having to gybe asymmetric boards, you simply have an opposite board in each hull and keep the windward one lifted and switch them when you tack/gybe

like you say angeling the board in relation to the hull would give the same affect to a symmetrical board, does anyone do this?

sorry thats beggining to sound like a bit of a rant