Upgrading to D600 with these lenses?

That's the oddity of some of the Tokina lenses. With the Tokina 12-24, from about 18.5 to 24mm, you'd be hard pressed to tell it is a DX lens. (The 18mm-19mm barrier seems to vary from sample to sample or user to user but that is where the boundary looks to be.) Once you go wider than that limit, you'll see the black box and internals creep into frame. Not much point in shooting this lens in DX mode since 12mm in DX is roughly the field of view you'll get in FX mode.