Speed also gets challenging with 650b also because of the wall created by the fat tyre being forced into the wind, it's not all rolling resistance. I don't mean to teach you to suck eggs.
I use continental race kings in 2" and like them a lot but because of that haven't ever really tried much else.
I'll say 'dry' but it's only because I'm prepared to sacrifice wet off-road grip for speed on tarmac.