Switch Systems for D600?

Sorry, I probably should have searched better before making this thread. From the samples I have been able to find with NR off, the 6D seems virtually identical to the 5DMIII at ISO 100 through about 800, with noticeably less noise from ISO 1600 on. Based on these images, I would be comfortable shooting with the 6D at ISO 1600 for astrophotography, and 3200 for landscapes.

Looking at DPreview comparison of the 600D to the 5DMIII, noise seems comparable throughout the ISO range, leading me to conclude that my comfort zone with the 600D would be ISO 800 both for astrophotography and landscapes (maybe 1600 for landscape depending on the composition).

Thanks to any who took the time to consider my question, and again, sorry for not looking harder for the answers before posting. I couldn't find those NR off comparisons between the 6D and 5DMIII ~10 days ago when I looked last.