That's probably another example of failure to revise the manual.
I've used my D300 in Yellowstone at -46 F. With the bare camera it failed in about 45 minutes. Failure is a rapid drop in battery charge as the camera gets really cold, then a loss of the AF sensor indicators, and then finally a failure to fire. The battery is the main problem, but I also had problems with my breath creating fog and ice at really cold temps. It took some time for the interior of the camera to warm enough to work properly.
We used a combination of heat packs or The Cozy Camera wrap to extend life. With the Cozy Camera and a couple of heat packs, I was able to shoot all day on a single battery at -20 F or more. Taping a heat pack over the side of the camera near the battery does a good job and worked for others.
The D600 will likely be no different. You need to be careful of plastic cracking from impact in extreme cold, but normally there is no real problem.
You need to take a look at the movie Chasing Ice which chronicles melting glaciers. It was filmed mainly with 27 Nikon D200 cameras in Greenland, Icelnd, and Alaska. http://www.chasingice.com/