No difference at all; I've tried it. Just make sure you're consistent in your timing between exposure and development; you'll probably see a difference if you expose the two grades an hour apart and then immediately develop because the paper slowly loses its exposure.

With a little math+experimentation and assuming you're printing uniformly (i.e. no dodges or burns that are different in each grade) then you can do it as a single exposure at an intermediate grade. Not much point though unless you need to produce a lot of copies.