I'm sure the a7R is a lot faster with the wide variety of native lenses currently available.
yes it is. And given your level of technical understanding, I am sure you appreciate this, as you are undoubtedly aware of the technical challenges involved to achieve similar AF-speed with FF-lenses/FF-sensors compared to much smaller sensors.
And ... looking at APS-mirrorless cameras, Sony A6000 and Fujifilm XT-1 show "very decent" AF-performance, including tracking-capability. Canon EOS-M? not at all. EOS-M2? neither.
And ... only 3 months after launch, 4 native lenses are currently available for Sony A7/7R
And ... 18 months after launch of the EOS-M? 3 native EF-M lenses ... only 2 for the US
And ... Sony has a roadmap showing which 15 native lenses will be available until 2015 and up to now they been delivering. Wouldn't it be nice to see such a roadmap for Canon EF-M lenses too?
And ... until then, the Canon EOS-M/EF-M is a rather "dead end".