The D700 has been proven over a 4 year period. I have two, and my only complaints are that I have had rubber coverings loosen twice now and the hot shoes are disasters if you use an SB800 or larger flash very often. I have read that some people are getting oil spots on one area of their sensor on the D600, from somewhere inside the camera. But not owning one, I don't know that to be factual -- so maybe I should not repeat that. But it's out there. All being equal, it gets you into an FX camera at a lower cost for a new body, although there are a growing number of really nice used D700s at some amazing prices. I may grab a third one soon!