Nikon 500mm f4.0 vs Canon 500mm f4.0

I have been shooting Nikon for almost 20 years (currently use D2x) and am considering buying the 500mm f4 lens but am rather burned up about the fact that Canon charges about 2,000 less for the same specifications and throws in "VR". It turns out that one can buy a 10MP Canon body, dedicate it to that lens, have the VR and still save money over the Nikon. Has anyone compared these two lenses.

I do a range of photography types and particularly like the bird photography, which is what I would use the 500mm with. I am currently using the Nikon 600mm AIS but mis the autofocus.

Joe Weissman