, vignetting and distortion test results from the Canon EOS 5Ds R
have been added to the Sigma 500mm f/4 DG OS HSM Sports Lens
Definitely follow (minimally) that first link. I think you will like what you see.
We do not yet have the Canon EF 500mm f/4L IS II Lens
tested on the 5Ds R but will have the Sigma results from the 1Ds III soon to make this direct comparison possible. However, the Canon 500mm f/4L IS II and the Canon 600mm f/4L IS II perform similarly and the Sigma 500mm f4 Sports vs. Canon EF 600mm f/4L IS II Lens comparison
is available now. B&H
has the Sigma 500mm f/4 DG OS HSM Sports Lens
in stock (Nikon F mount is on backorder).