Greetings from the "Dark Side" This comment may be considered to be biased, considering that I am a Nikon user, but much of my view could equally be exploited by Canon wildlife users that have a substantial investment in pro-level glass.
Timbo, since the last post you made on this site regarding your equipment, it would seem that you have a substantial investment in glass across the range, but none of it seems to be at a pro level, and your camera could also be considered at consumer level. (Canon 550D?). Clearly you have both the passion and the ability and I like the images of yours that I have seen so far. However, I would suggest that you seriously consider your needs, both in the short and medium term, when it comes to photography.
So what are you currently lacking in your set-up that requires you to upgrade and what will any of the new bodies give you that you do not have, AND you would like? Would it not be better to invest in better glass, and when you have exhausted that opportunity, to then upgrade to a better, more suitable body when the need (and budget) arrives?
Have a look at the dxomark.com website to compare sensors on various DSLR cameras. On a general rating, the Nikon D7000 is rated higher than the 7d and the Nikon D600 trumps both the 5dmkII and 5DmkIII and is only 2nd to the D800, which is considered the best sensor in ANY DLSR.
As a wildlife shooter, should you move from DX to FX, you will have to get additional, longer lenses to compensate for the "loss" of the crop factor. Sure, you can crop any FX image, but that is not a viable reason to move to FX. You will lose the frame-rate that you may want, but you will certainly gain on the low-light capability.
All bodies have trade-offs in of some sort and you just need to define your needs and wants, realising that a substantial investment in glass is going to be required to extract the best out of any body that you choose. Unfortunately for you and the rest of the canon users out there, NIKON seem to be at the top of the pile when it comes to sensor performance in both the DX and FX arenas, at least for the moment.