There has been a debate on some online forums as to whether a camera with a much higher pixel density can produce a decent high ISO image as one with a lower pixel density (assuming the sensor size is the same). In particular people were wondering if the Canon 1Ds3 can produce usable images at high ISO compared to the Nikon D3 (one of the features is the ability to shoot at ISO 25600, albeit rather noisily). I happened to be able to get access to both of these bodies with similar lenses, so I compared the two. My review can be found on my site:
1Ds3 vs. D3 High ISO
So what's the conclusion? You'll have to read the review to find out :)
Technical Specs: Canon 1Ds3, 70-200 f/2.8 @ 70mm, f/5.6, 1/640s, ISO 3200 (digitally pushed 3 stops).