Back OT, after a morning shooting over 1,000 shots with my 7D I realized that I'll likely continue as I am, with a 5D and a 7D, but update both as updates become available. So, I'll buy the 5D MkIII in the summer or fall and the 7D MkII when it comes out.
With the Digic-5 processor and slightly improved sensor, the 7D should be the cat's meow for nature shooting. It doesn't look like there'll be a 1D MkV and the 7D2 is likely to be superior to the MkIV (the 7D already is in certain regards, like pixel-pitch), the huge pixels on the 1D X won't cut it for nature and, although the 5D3 will indeed "cut it", the 7D and 7D2 will be superior in detail resolution and likely quicker.
That will also mean that I'll stay with my 500mm lens a while longer. With FF I would have felt pressured to go to 600mm, but now I can wait do a trial comparison of the Series II 500mm/600mm, once I've got my new bodies in hand, perhaps a year down the road.