some 5D guys are extremely insecure and condescending, hating the 6D just like some die hard D8xx fans hate the Sony A7R or D610.
but it all depends on what you shoot or what how much weight you like to carry with you regardless or tiny bit of AF feature set difference between the 2 in question here.
but one thing I am sure about is the 6D's center point AF is quite much better than any AF point of the 61pts of the 5D Af sensor or D810 sensor.
I tried many times in lowlight and nothing with the mirror beat the 6D in the area of lowlight AF.
The GH4 and the A7s are better than the 6D in this specific area, but none of Nikon Canon with mirror beats it.
Oh and also for long exposure thermal noise, the 6D is about 34 percent better than the 5D3 , you can see it in all sensor tests including Roger's.
Some guys just really don't want to admit 6D's sensor IQ superiority in low-light. Well, if it's AF that's more important to them and what defines "HIGH ISO KING", then so be it. We can't argue on something where our definition differs.
It really hurts when you invested some more $$$ just to find out that it's not superior in everything to something that's significantly cheaper.
Correct, but the 6D also suffers from that 'disease' as the outer AF points of even the T5i are better than those of the 6D.