Being a recent convert from the DX D300's to FX D800 and D600 I personally don't think you can go wrong with either, both are magnificent cameras. My wife and I both primarily shoot Wildlife as well, using the D600 as a back up with a smaller lens attached when close proximity to our subject demands. We have been staggered to see the wonderful detail that the D800 allows with 36m pixels. Yes the files are large, but having those additional pixels when shooting wildlife allows out of camera cropping without losing any of that fantastic detail. Yes, the D800 needs a well practiced technique, but those additional 12m pixels will produce shots you probably never thought you were capable of getting. U cannot comment on the D7000 having never used it.