... believe it or not, using the focus peaking feature, the a7R with a cheap adapter is actually much faster then the autofocus on EOS-M with its native lenses. I've had the EOS-M for almost a year and made over 30000 images with it, and I was very satisfied with it's image quality ... but after having tried some of the competing mirrorless cameras, I sold the EOS-M last week ... now I plan on getting a Panasonic GX7 and a Sony a6000 ... pretty sure of getting the a6000 (when it is released), but I'm still undecided about the GX7
Did you update the firmware on your M? I thought that made a significant improvement, and certainly faster than what I can achieve (at least with wide apertures) manually on my A7r (not that speed is usually an issue for me); though of course you may be much more adept at mf than I am....
As for the GX7, it certainly has its admirers, but its IBIS isn't nearly as good as that in Olympus bodies (esp. the OM-Ds), and the one I briefly owned never made images that looked as sharp as those I get from my Olympus - but maybe I had a bad copy.
Meanwhile, I suspect this post is closer to the truth than many around here would like:http://soundimageplus.blogspot.co.uk/2014/03/when-is-dslr-not-dslr-when-its-sony-a7r.html