I would agree the D600 ISO proformance is outstanding and it would kick the d700 in the teeth
Well thats serious rubbish youre spouting there, i have owned both and sent the D600 back and re bought a D700.
The D700 kicks the 600's ass in the speed and accuracy of the AF, the 600's af points are crammed into the middle of the sensor so using centre AF with assist points selected is useless if moving subject veers off to one side of the frame, the 700 will keep up with this as the AF points cover a much larger area
The D700 i regularly used at ISO 6400 under floodlit night matches and it coped extremly wekk and noise wasn't any issue, the 600 couldnt even get a lock onto its subject under the same conditions.
As for the noise, if you sampled the 600 files down to the same as the 700, the 700 was a clear winner at ISO 3200 and 6400
Should add for balance that the 600 does produce much nicer images at lower ISO's and the dynamic range is a very nice improvement over the 700 as well
These findings are just my own personal views on owning both cameras at the same time, im sure you can point me to websites which will contradict my own findings but please dont bother, like i say there are just my own personal findings.