It would be a 24-70mm f/2.8L IS or (or maybe and?) a 24-70mm f/2.8L II, since there's no current/MkI version of that lens with IS. I, for one, would prefer IS to go along with improved coatings and optics.
the whole world is waiting for 24-70 f2.8L IS. seriously. not 24-70 f2.8L II - what is that? there will zero people going to buy that just to get a little improvement in IQ. 24-70 f2.8L already a fantastic lens.