"Perform" is a term that means different things to different people. If "performance" means faster/more accurate AF, or better high ISO capabilities, etc. then, sure, the 5D III outperforms the a7 and a7R.
I wouldnt even subscribe to that. While my 5D3 clearly has faster AF in most situations, it is not as accurate as the sony. That little gem almost never misses a shot and the face-af just snaps on the the eye, it even manages backlight very well. i am still very impressed with it and -for my work- it even works better than the 5D3 in some (not any of course) cases.
and the sony has much less shadow noise, you can push those files pretty brutal without getting any of that blotchy color banding stuff the canon sensors do even at low iso.










