I don't understand you guys, when you are comparing 6d with 5d mark3. it's different products. the 6d is for the people, who was shooting with cameras like 1000D, or 600D and they just want better image quality in low light, or have wider angle. if you will compare the 6D auto focus with my old 550D, then it's insane fast. i am using only center point in both cameras, and the focus speed is about 2x faster. example: i have 100mm macro f2.8, not L lens. with 550D i can't shoot slowly walking people, but with 6D and the same lens, with the center point only, i can shoot like this easy:
my friend with the bike was moving really fast. and i done about 5 shoots continuously. all in perfect focus. jpg, strait from the camera.
the video is bad, i know. but again, if you was shooting video with old camera, you have now possibility to shoot at 12.800 iso easy or even in 16.000, and have the better result than 550D in 3200 iso. so it's more than 2 stops of additional light, and still better quality. and if i was a film maker, i will not buy the 6D and no one buy it for video. but to film my life around, it's perfect.
the one thing, the camera is bad, is that you cant keep the exposure in one level. if you shoot few frames in Aperture mode, same object, you will have +-1 Ev in your shots. sometimes less, sometimes more. it sucks. but that's only bad thing for me.
the camera is not for people, who want to use it as a job tool. but for hobby more. and in hobby you don't have something to important to need second card slot, or 60 focus points and so on. so it's perfect camera for 3 or 4 years.
Don't forget those already on FF that need a decent backup body! the 6d is a fine companion to the 5d3! I probably wouldn't be complimenting the 6d as much if that was my only FF body, because I can use the 6d up until i hit the wall of its features (IE, if i am shooting wide open on a prime lens in the sun, yeah, it may be time to set the 6d down and pick up the mk3 because I may need to go over 1/4000th. If i am shooting at a wedding, reception, dancing, I may want to switch to the mk3 for fast moving dancing, because the servo mode is not so good. If i am in low light, using ambient light only and want to frame the subject to the far left or right, yeah, time to set down the 6d. So my analysis of the 6d is based on my use, if it were my only FF body I'd most likely find the limitations frustrating, but, it does do what i want it to do quite fine and the mk3 can pick up the slack for what the 6d can't do....