I just got my A7s which was a hard decision after only ever shooting Canon. But the very few tests I've done are pretty amazing between the two cameras. I hope Canon makes me regret buying the A7s soon! Here are my first few tests.
1. A7s vs 5D mkIII: Basic Tests
https://www.youtube.com/watch?v=ZiRw-yr-4TE&list=UUwdaupRfZzUCkoFWIrEoF8Q
2. A7s vs 5D mkIII Slo-mo
https://www.youtube.com/watch?v=gKMTHc8lpUE&list=UUwdaupRfZzUCkoFWIrEoF8Q&index=2
3. A7s First test: just playing around and getting to know the camera
https://www.youtube.com/watch?v=ad__F0NR5L8&list=UUwdaupRfZzUCkoFWIrEoF8Q&index=3
1. A7s vs 5D mkIII: Basic Tests
https://www.youtube.com/watch?v=ZiRw-yr-4TE&list=UUwdaupRfZzUCkoFWIrEoF8Q
2. A7s vs 5D mkIII Slo-mo
https://www.youtube.com/watch?v=gKMTHc8lpUE&list=UUwdaupRfZzUCkoFWIrEoF8Q&index=2
3. A7s First test: just playing around and getting to know the camera
https://www.youtube.com/watch?v=ad__F0NR5L8&list=UUwdaupRfZzUCkoFWIrEoF8Q&index=3