I was a 5D3 user and that was my workhorse camera for everything i shoot and i love that camera.
However, i wanted something smaller and lighter and since i was on FF, i needed it to be FF and I can't afford a Leica.
So in a way, the Sony A7r was what i always wanted.
I spent an hour today with the A7r and the A7 and comparing to the 5D3, the AF is definately not as fast but it's not slow either.
The continuous focusing is no where near the 5D3..it fails quite miserably actually but thankfully what i shoot, i don't use continuous AF. Surprisingly, i find the A7 even slower to focus than the a7r with the same lens.
The EVF is still not as nice to look at compared to the OVF but i guess you get used to it.. IQ however, even SOOC, that's where the 5D3 even with a good prime can't match the A7r.
Ultimately, if you are looking at something to dethrone the 5D3, this isn't going to do it except in terms of IQ. Everything else, i think the 5D3 is better.
But for me, it's light, REALLY small in the hands, fantastic IQ even SOOC jpg and it's exactly what i need for what i shoot.