Waiting for the D400? You're not alone...

Low light AF capability is important but the 39 points vs. 51 points is really almost no difference IMO if you look at the coverage and consider how most people use their AF.

http://photographylife.com/wp-content/uploads/2012/10/Nikon-D600-vs-D800-Viewfinder.png

Is the D600 slower and less accurate when compared to D800 or even the D700?

I guess someone needs to do a through comparison.  Unfortunately, I do not own either but am planning a purchase later this year.