“DigitalCameraInfo”:http://www.digitalcamerainfo.com/content/Nikon-D200-vs-Canon-EOS-5D-Head-to-Head-Review-.htm does An interesting comparison of the two cameras. A littl unfair since the 5D is so much more expensive and the review says you get what you pay for. At $3000 street, the 5D is the better camera if you can afford it particularly at ISO above 400 and with just that bit more detail.
In the key “Image quality”:http://www.digitalcamerainfo.com/content/Nikon-D200-vs-Canon-EOS-5D-Head-to-Head-Review-/Performance–Image-Quality.htm
Perhaps not surprisingly, the difference between 10 megapixel Nikon and 12 megapixel Canon wasn’t that much when at f/1.4, bu t when stopped down at f/8. This is quite visible in an 8×10. Color-wise, Canon is more accurate out of the camera, while Nikon is oversaturated to appeal to consumers, but notes that you should set the 5D to RAW, while D200 processes JPEGs better.
http://www.digitalcamerainfo.com/images/upload/Image/H2H:%205D%20-%20D200/H2H%20HTML/5D200-50mmf8-ResGR.jpg
In terms of noise, the D200 is much noisier above ISO400, but by ISO 500 and above, the full frame sensor is much better, so it is better in low light.