– At ISO 204,800 and beyond the A7s has up to a 2 EV advantage
– At Moderately high ISO performance the A7s has up to a 1 EV advantage in shadows
– No difference between the cameras at low ISO.
At the end their conclusion is:
The Sony A7S enables the use of incredibly high ISOs, including some unavailable to most cameras. When shooting at incredibly low light levels, the A7S will most likely give you significantly better results than any camera that does not natively shoot at these ISOs. There are also some advantages to be had over the higher native ISOs of the cameras we tested: we see the A7S overtake the A7R in normalized shadow noise performance at ISOs above 6400 in our tests. At more moderately high ISOs (6400 and below) as well as in brighter regions of images – where image quality is determined primarily by how much total light is captured – the normalized ISO performance of the A7S will be similar to that of full-frame cameras of its generation.
The A7s manual can be downloaded at support.sony-asia.com.edgesuite.net/consumer/IM/4537940111.pdf.