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I expect the D600 to have superior imaging ability, but the D700 is a different class of body, which has picture-taking relevance beyond just the computer inside.
What do you mean by that last paragraph?
I’m talking about camera features that won’t directly affect the quality of a picture. For example, the D600 doesn’t appear to have an eyepiece shutter or sync terminal. There are ways around those shortcomings—it’s not the end of the world—but I wouldn’t choose to work around something that was already well executed in the past. Still, we can probably count on the D600 beating the D700 in imaging specs. Better DR, lower noise, etc...