Sony A7R delivers, even at high sensitivities (photo samples)

You can start to see a tiny bit of processing artifacts at ISO 800, but I consider it quite clean.
Lab tests performed with the Zeiss Sonnar T* FE 55mm F1.8 ZA; field tests performed with that lens as well as the Sonnar T* FE 35mm F2.8 ZA.

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 really see the difference between the sensors in the A7 and A7R.

I really like the Zeiss 55mm f1.8 ZA lens in general, and it plus the camera delivers soft, smooth and round out-of-focus highlights.
(1/80 sec, f3.5, spot metering, AWB, ISO 100, 55mm)

Given the distance I was from the squirrel with a not-very-long lens, the detail resolution looks quite good.
(1/60 sec, f5, multi metering, AWB, ISO 100, 55mm)

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)

JPEGs at ISO 1600 show some smearing on textures, but can still retain quite a bit of detail.

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)

You can get some increased sharpness by processing raw starting at about ISO 1600.
(1/80 sec, f2.5, multi metering, AWB, ISO 3200, 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)

I wouldn't use the JPEGs full size at this high a sensitivity, but they're serviceable scaled down, and shooting raw lets you recover more detail.
(1/80 sec, f5.6, multi metering, AWB, ISO 12800, 55mm)

In its default settings, the A7R renders pretty accurate colors.

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)

The default Standard Creative Style shifts hues a little, but doesn't push contrast too much.