The exposure factor of +2 was moderated by using -1 in ACR processing, but was not colour clipping at +2 because of the white diffused nature of the subject and light. A straight exposure would have resulted (and did result) in a very dark image, exposed in real terms more at 12,800 than 6400. The +2 exposure produced a right-end histogram clipping but ACR had no trouble getting back this amount of headroom, which indicates a good dynamic range and overexposure tolerance even at ISO 6400.
This is a full size conversion using ACR 4.6 (not necessarily the best converter) from a cRAW file with High ISO NR set on the camera to Normal. No sharpening has been used, and no luminance NR, but chroma NR was set to 50.