I think that since the DAT really tests on very basic principles and concepts (especially applies on O-chem), you're better off knowing those really really well. I think that i went a bit overboard on my reaction memorization, which was totally useless. However, they(DAT dudes) do find creative ways to ask you (and mask) those basic concepts... So just know them well, and you'll shoot way past a 20.
(By basic concepts, I'm really talking about SN1, SN2, E1, E2, and ox/red reactions)