Good low-light AF performance may be near-useless if the sensor cannot read the photons well enough (ISO performance), and in that regard I'd say the D600 should run circles around the older cameras mentioned.
That said, I do recognize the need for low-light AF, without the annoying assist light, sometimes even for speedlight work (think strobism).
I have found the D600 to focus accurately in every instance I needed it to, with no complaints. For the record, I use back-button, AF-C, most often on 9-point dynamic, center point, focus and recompose.
http://egozarolho.blogspot.com 1. Good content, good aesthetics and good tecnique. On that order. 2. Light is more important than glass and pixels. 3. In the digital photography process, software is as important as gear.