This is very interesting information supplied to us by doodah in another thread:
On another note,
Lens Rentals decided to put AF consistency of various Canon cameras to the test using a recently released 28 f/2.8 IS lens in single shot mode. This is what they obtained for the standard deviation of AF accuracy, a measure of AF consistency:
1DsIII 29
5D II 38.5
50D 34
7D 41
1DIV 22
60D 34
T3i 41
1Dx 17
5D III 17
T4i 29
6D 28
We can group Canon DSLR AF consistency into 3 groups:
Tier 1: 1DX, 5D3 (as good as live view when the latest lenses are mounted)... 1D4 trailing slightly
Tier 2: 6D, 1Ds3, T4i... 50D, 60D trailing slightly
Tier 3: 5D2, 7D, T3i
So, 6D is about as good as the 1Ds3, but not as good as 1DX and 5D3.
PS: Do not be shocked by the poor AF consistency of the 7D in single shot mode because that agrees with my personal experience too.