Hmm. LensRentals did a controlled test and the results don't support your enthusiasm.
In terms of AF accuracy, the 6D is closer to the 5DII than the 1DX/5DIII.
I don't think Roger Cicala was being consistent in the above article.
If we list the AF standard deviations of previous Canon cameras tested by Roger using the new 28 f/2.8 IS USM, this is what we get:
5D II 38.5
5D III 17
If we group them according to AF consistency of the center point, this is the result:
Tier 1: 1DX, 5D3... 1D4 trailing slightly
Tier 2: 6D, 1Ds3, T4i... 50D, 60D trailing slightly
Tier 3: 5D2, 7D, T3i
So, yes, the 6D beats out the 5D2 (and the 7D too... consistent with my experience).