Stumbled across a post from a Chinese photography forum with high ISO pix by Nikon's D3 preproduction unit. The OP of that post allows usage of the photos but requires stating the soucre.
Please make your own observation and draw your own conclusion.
Edit: NR off
ISO 200 100% crop
ISO 400 100% crop
|IMAGE IS A REDIRECT OR MISSING!|
Byte size: ZERO | Content warning: NOT AN IMAGE
ISO 800 100% crop
ISO 1600 100% crop
ISO 3200 100% crop
ISO 6400 100% crop
ISO 8000 100% crop