I picked up a D600 this weekend and was playing around in the backyard, photographing my dogs running around. I used AF-c, 9 point, then went to single-point and found I was getting sharper images. LOL
When you have AF to AUTO, do you mean the "3-D" tracking or whatever it's called?
One of the first things I note about this is the burst rate. During the time my D200 was in the shop, I used my boss' Canon 7D, and 8FPS v 5.5 (even 6 in my D200) is very noticeable. Compared to her new Canon 1Dx (at 14fps), it's downright a 3-toed sloth in comparison.
Doing some comparison shots v my D200 this week to see the difference in IQ, etc.