There are lot of explanations/comparisons of auto focus capability of different cameras available.
Canon 5D Mark III has been termed as a superior camera for this feature in the semi-pro range. In this aspect, how can the difference be described between 6D and 5D Mark III?
Are there any photo examples online for comparison between both the cameras and possible scenarios[roughly mentioned as sports/photography]. Examples of a few shots using Mark III which can't be achieved using 6D/Mark II?
There's never going to be a shot which can't be achieved on the 6D or the 5D Mark II due to the lesser AF capabilities of those cameras - with enough precognition (also known as experience), you could have manually focused on exactly where the action was going to occur and not needed any AF at all.
That's not to say that you won't get a higher proportion of high quality images when using a better AF system, just that it's a mistake to look at it in terms of making an image possible when it wasn't before.
With Phase Detection Auto Focus it is ultimately about how accurate the system is. To put it another way, it is all about how often the the system is accurate enough. Every system will have variation from one shot to the next. The question is what is the average difference from sharpest focus for each shot.
The best single place I've seen describe the differences between various Canon bodies in terms of AF is a blog entry by Roger Cicala at lensrentals.com. The 6D wasn't out when he did his data collection, but I'd be surprised if it was much better than the T4i in this respect. With a current generation lens design, he found that standard deviation for the recent 1D series bodies and the 5DIII was about one half that of the other recent Canon bodies.
Please note that the lens plays just as large a role in AF accuracy as the body does. The weakest of the two components will determine the best each combination will be able to perform. A 5DIII or even a 1D X will do little better than a T3 if a lens like the much maligned EF 75-300mm f/4-5.6 is mounted on it.
