I would expect you'd find great lens speed *less*often useful/necessary, given the higher ISO and better AF, but they still have their place, especially if you really like that very-thin DOF. I've always liked fast lenses for the snappy manual focusing, primarily, and usually like to keep em around f2 or 2.4, anyway, if possible, both for the better sharpness and cause that's about where I usually want my narrow DOF, anyway. But that's a matter of taste and all.
If you really like the really narrow DOF option, of course you'll want your faster lenses: not much getting around that.