Well, there's not much doubt about the AF on the E-M1 - fast and accurate, it's the tracking that lets it down - to be honest, I think that all the mirror less cameras seem to have fast and accurate single shot focusing, it's continuous that isn't.
I must say that in my experience the AF tracking of the EM1 works pretty well if set to AF area of 9 AF points. It is not quite up to the Nikon D800E, but not too much different. And I tested with the 75-300 II and the 12-40. Especially at 300 I was surprised how good this works. Actually this is one of the main reasons why I am keeping the EM1, as it gives me kind of what I am looking for in AF tracking for wildlife. Only a faster super telephoto zoom would be really on my wish list!
Having said that - if set to single AF point or even "small single AF" point it really sucks. But then also D800E gets worse if only using a single AF point.
IMHO the EM1 is lightyears ahead of the Fuji's (name your favorite) and I cannot speak for the A7/A7r as I did not test AF tracking there.
No doubt the next generation(s) of mirror less cameras will outperform classical DSLRs, I would bet even the D4s and D1X likes.