Interesting replies.

So question 3 is:

Isn't the pixel density between a 16MP DX sensor and a 24MP FX sensor essentially the same? (that's sort of a rehtorical question since I was an applications engineer for immage sensors). The answer is not really as 16 x 1.5 = 24.

Any gain in iso would be in a tighter control of noise in the ADC's, and signal path, or better in-camera processing, but at this point I'm not sure how much better that would be.

And finally the sweet spot of any lens radiates from the center with diminishing returns as you move outward. This being the case I would have to believe that a DX camera would better utilize a lens built for FX sensors as the crop would eliminate the typically weaker lens perimeter.

Anyway, the bottom line is: would I expect the D600 to be a better immager than the D7000? Maybe marginally, but on the whole probably not. For sports shooting? Definately not. With similar ISO characteristics, slightly faster continuos shooting, and the extra 1.5x reach, better use of the lenses sweet spot, as well as a faster maximum shutter speed I would think the D7000 would still be a better sports camera.