>I recommend to go to a store, even something like Best Buy, >and hold either camera in your hands for a minute. I did, and strongly preferred the D800. Others may come to the opposite conclusion, or be ambivalent about it, but handling matters, >at least in my opinion. <Quote<<<
The D600 is lighter and fits my wife's hands better. For me the handling of the D800 is so much better that I can hand hold it much longer at an Event before getting tired. The narrow groove in the D600 grip pinches my fat fingers. I also like the button layout better.
I have not noticed the High ISO being any better on the D600 and I have the frame rate set for 3fps so my wife does not take double shots. So, for me everything is better about the D800.