“David is an avid Nikon shooter, and currently owns several Nikon D3 cameras. Meanwhile, Robert owns and shoots Canon, including a number of 5D Mark II cameras and many of Canonâ€™s sharpest L-series lenses. In this â€œUnique Photo Shootout,â€ we placed the latest and greatest from their respective brands in their hands, and put them in one of the toughest shooting environments we could find. David was given a Nikon D3s and Nikon 400mm F2.8 VR lens, and Robert had a Canon EOS 1D Mark IV with a Canon 300mm F2.8 IS. Since the Nikon D3s is a full frame camera, and the Canon EOS 1D Mark IV has a crop factor of 1.3x, this gave both photographs about the same focal length equivalent”
Read more at uniquephoto.blogspot.com with several nice comparison shots and you can download full size images as well.