Compared to...

Studio scene comparison (higher sensitivities)

With 'only' 12 million pixels on a full-frame sensor the D700's individual photo sites are comparatively large (1.4 MP/cm² pixel density on the D700 vs 2.9 MP/cm² on the Sony A900) and the Nikon makes exceptionally good use of its large pixels' light gathering capabilities. Combine this with Nikon's sensible approach to noise reduction which tackles chroma (color) noise first and then applies relatively mild amounts of luminance noise reduction, and you get a camera that is an outstanding performer in low light.

The D700's high sensitivity images show some visible luminance noise (grain) but are looking more detailed than the competition's. The gap widens as you go further up the sensitivity scale and at extreme settings such as ISO 6400 and higher the D700 (and the D3) are completely in a class of its own.

Obviously the D700 is also the only camera in this comparison that offers ISO settings higher than 6400. So, if you actually need these extreme sensitivities (Available light cave photography maybe?) there's not an awful lot of choice (The Canon 5D Mark II offers ISOs up to 25600 as well, we'll update this review as soon as we've got a reviewable model).

ISO 1600

Nikon D700 Sony DSLR-A900
Canon EOS 5 Nikon D300

ISO 3200

Nikon D700 Sony DSLR-A900
Canon EOS 5D Nikon D300

ISO 6400

Nikon D700 Sony DSLR-A900
 
  Nikon D300

D700 High ISO settings

Nikon D700 ISO 8000 (H 0.3) Nikon D700 ISO 10000 (H 0.7)
Nikon D700 ISO 12,800 (H 1.0) Nikon D700 ISO 25,600 (H2.0)