The definition of "low light" is critical to these conversations
Furthermore "achieving focus" needs definition, because in problematic lighting conditions the camera will take more time to focus - I hope the detailed dpreview.com 6d review will tell us at last if the -3lv rated 6d is getting a focus lock faster @-2lv than the 5d3 which is maxed out in this level.
It should based on the theory. As I normally shoot in the evenings / night, I am really looking at the 6D as a replacement for the 7D if this is confirmed. Too bad in my country there is no option of renting the 6D or I would have checked it out by now.
For me the AF issues have arisen only in near darkness situations. The AF seems to continually hunt from end to end. Otherwise the AF system is near perfect.
1DX, 5D3, 600D, RX100
16-35L, 24-70L II, 70-200L II, 100-400L II, 50L, 85L II, 135L, 17TSE, 24TSE, 40, 100 macro, 18-55 II, 55-250 II, 1.4x III, 2x III, 600RT x 4
When it comes to gear, it is better to vote with your wallet. Bitching on online forums like a lunatic doesn't get you anywhere!