Interesting. I too found the Sony seemed to have a little focus breathing going on, not much, but at close range the Canon did have slightly more magnification.
As for sharpness, I just looked at the results again and I can't decide which is better. It's so freakin' close. One moment I think the Sony has the edge, the next the Canon, then it looks about the same. Even with the TCs I'm just not seeing much if any difference. Super close... (Although I didn't compare 2X since I don't have one yet for the Canon).
What's really impressive is how close the 200-600 is to the 600 F/4 GM. Don't get the wrong, you can spot the 600 F/4 pretty quick, but the 200-600 isn't as far behind as I would have expected - it's really goof.