Which is better? A Nikon D600 or D800? Mostly using it HANDHELD & with low light.

I do not have the D600, but have the D800e and D7k.  I also had the D700.

Clearly, you do not need the extra megapixels of the D800, so I think the questions comes down to ergonomics and functionality.  My view on the motion blur is that the pixel density of the D7k and D800e are close and if you do not have problems with your D7k, then you shouldn't have problems with the D800e.

Here's a few things that has not been mentioned.

• The bigger/heavier body of the D800e can result in less motion blur because I find it more stable.
• The crop modes of D800e could save you quite a bit of time unless you print to 4x6 most of the time.
• I switch between autoiso on/off quite a lot and I find it much easier to do on the D800e