maziarrezaei: As far as I could see, A7S and the other higher res cameras perform equally in sane ISO levels.
There is one area missing in this test. One can argue that if an X amount of noise reduction is applied to all images, and then they are normalized down to 12MP we can achieve better results with 5DII & A7R. I'm speaking of ISO levels of 6400 and lower.
Duly noted Rishi!
By lower ISOs I mean the normal range 1600 to 6400 that the noise level is noticeable. I think when you do NR on a higher res image you can do better in terms of the granularity of noise detection that you can't do with a lower resolution. I can sure put it to a test!
As far as I could see, A7S and the other higher res cameras perform equally in sane ISO levels.