13. USB 2 not USB 3
This is odd. The D800 has a USB 3 port compatible with USB 2, but the D600 is USB 2 only. USB 3 is rapidly emerging as the new standard, and the D600 is ahead of the game in other technical respects, so its USB 2 interface seems at best an oversight and at worst a mistake.
14. Batteries and grips
The D800 and the D600 use the same EN-EL15 battery, but the D600 needs a new battery grip (the MB-D14) because of its new, compact design, whereas the D800 uses the MB-D12. The MB-D12, incidentally, boosts the D800’s continuous shooting speed to 6fps, which makes it slightly faster than the D600 with the grip fitted (which shoots at 5.5fps with or without the grip).
15. Flash connectivity
The D600 and D800 both have a built-in flash, and both have Nikon’s commander mode for controlling external Speedlights wirelessly. The key difference is, though, that the D800 has a PC sync socket, but the D600 doesn’t. This is a problem if you want to use a ‘wired’ studio lighting system (forcing you to buy a hotshoe adapter).
16. Nikon Professional User scheme
Nikon’s Professional User (NPU) scheme will be little-known to amateurs, but it’s an important service for many professionals, including a dedicated support line, discounted training, a regular Nikon Pro magazine and more. The point is that you need two items of pro Nikon kit, and while the D800 qualifies, the D600 does not. Nikon Europe’s website lists the D600 as one of its ‘consumer’ cameras.