Compared to...

Studio scene comparison (higher sensitivities)

Nikon's approach to noise reduction has always been chroma (color) noise reduction first, then relatively mild amounts of luminance noise reduction. This tends to leave its high sensitivity images looking more detailed but with potentially more visible luminance 'grain' noise (which isn't generally as objectionable as the more digital-like blotchy color noise). There's no doubt that the D3 is the winner once you get above ISO 1600, and that its output remains usable right to the top of its extended range. We were continually impressed by the almost 'film like' grain exhibited by high ISO D3 files (as opposed to heavy digital noise reduction).

It's also worth mentioning that all the cameras here - even the D300 and EOS-1Ds Mark III with their densely-packed sensors - produce high ISO results that would have been unthinkable a few years ago, giving photographers the kind of flexibility they could only dream of in the days of film. Where the D3 really impresses is at the extremes - ISO 6400 and above - at which point it really does set a new benchmark; not only for low noise, but for detail and (importantly) color accuracy. It may not be a quantum leap (there's only so much you can expect at these sensitivity levels), but it's impressive stuff.

ISO 1600

Nikon D3 Canon EOS-1DS Mark III
Nikon D300 Canon EOS 5
Canon EOS-1D Mark III  

ISO 3200

Nikon D3 Canon EOS-1DS Mark III
Nikon D300 Canon EOS 5D
Canon EOS-1D Mark III  

ISO 6400

Nikon D3 Nikon D300
Canon EOS-1D Mark III  

D3 High ISO settings

Nikon D3 ISO 9000 (H 0.5) Nikon D3 ISO 12,800 (H 1.0)
Nikon D3 ISO 25,600 (H2.0)