I have been testing the D3 all week and in my opinion it is f
ar better than any of the Canons, and this is from a dedicated Canon pro.
The high ISO performance is better IMHO than the 1D MK3, so is the autofocus. The images also have a much better dynamic range, one look at the histograms compared to the 1DS MK3 show that. I have been shooting both cameras alongside each other and I have given up the MK3 as it is too slow to do much
http://www.technologically.net/nikon-d3/andy-rouse/