Just been playing with the D4 for the first time this weekend. Noise performance is pretty good at ISO 12,800. These were just saved as JPEGs by the camera, no post-processing.
NB These are not great photos, just ones where I used ISO 12,800 (which wasn't very often).
[url= http://farm8.staticflickr.com/7086/7400850484_ab713aa37f.jp g" target="_blank">
[url= http://www.flickr.com/photos/brf/7400850484/ ]St. Mary Basilica[/url] by [url= http://www.flickr.com/people/brf/ ]brf[/url], on Flickr
[url= http://farm8.staticflickr.com/7094/7400853222_dc2104abe1.jp g" target="_blank">
[url= http://www.flickr.com/photos/brf/7400853222/ ]St. Mary Basilica and main square[/url] by [url= http://www.flickr.com/people/brf/ ]brf[/url], on Flickr
Looks good, how 'dark' did it look in real life and what shutter/appeture did it need?
You can see the EXIF info in Flickr. The longer distance once were at F2 with about 1/60s exposure. Hand held, I try and stay above 1/60 although I can get decent stability down to about 1/30 esp with the bigger camera body.
EDIT Basicalla one was:
Exposure 0.006 sec (1/160)
Aperture f/2.0
Focal Length 50 mm
Focal Length 50.4 mm
ISO Speed 12800
Exposure Bias 0 EV