The 500mm and 600mm viewed from the front.
Both are gems of glass from Canon. With the extra
100mm the pictures from the 600mm is 44% larger
than that of the 500m. No brainer for me to get the
600mm as well. And the 500mm? It belongs to my
wife now!!
Both units sold, my wife and I have our own EF800mm each as of Sep 2009.