Quick question for people using live view focus on D800 and/or D600

Actually, no. In low light PDAF is better. PDAF also offers better camera stability so one can shoot at slower shutter speeds, but sure, when the camera can AF it always nails the focus.

One huge advantage of the D800 is the built in eye piece shutter, which is a must if the exposure is important, especially with the sun in your back. The D600 does not have that shutter.