Shadow detail starts to suffer at ISO 1600; you can see some processing artifacts on well-illuminated detail at that point, but no serious detail degradation until about ISO 6400.
You can see artifacts, but the camera retains sufficient detail to be able to render readable text at this distance. It looks clean and sharp printed at 13x19 as well.
(1/80 sec, f2, multi metering, AWB, ISO 800, 55mm)
As ISO sensitivity rises, a camera tends to increasingly clip highlights. The A7R preserves quite a bit of detail in the highlights that you can recover by shooting raw. (Whoops. Forgot to label the shot: raw on the left, JPEG on the right.)
(1/10 sec, f2.8, multi metering, AWB, ISO 1600, 55mm)
Normally it's quite difficult to recover any shadow detail in high ISO sensitivity images; while I wish it hadn't been lost by the JPEG, you can see it's still there.
(1/200 sec, f5, multi metering, AWB, ISO 6400, 55mm)
While the camera definitely shifts hues in JPEGs with oversaturated reds, it still retains detail in the oversaturated areas. Raw shots are more accurate.
(1/80 sec, f6.3, multi metering, AWB, ISO 100, 55mm)
