COMPARED @ 24mm: Canon EF 24-70mm f/2.8L II vs EF 24-70mm f/4L IS
Added to my review of current Canon 24-70mm L zooms is a first comparison between the 24-70mm f/2.8L II and the 24-70mm f/4L IS. I have several more comparisons coming.
B&H Photo has both the 24-70mm f/2.8L II and 24-70mm f/4L IS in stock.