You are going to like this: Image quality results from the Canon EOS 5Ds R have been added to the Sigma 85mm f/1.4 DG HSM Art Lens Review page.
I'm guessing that you are impressed with what you see, but the Sigma 85mm f/1.4 Art Lens vs. Canon EF 85mm f/1.2L II Lens comparison should fully convince you.
Results from the Canon EOS-1Ds Mark III and Canon EOS 7D Mark II are coming and will make many additional comparisons possible. But, this lens is certainly looking impressive from an image quality perspective!
Make the Sigma 85mm f/1.4 DG HSM Art Lens your Christmas present! B&H has this lens in stock (Nikon) and "coming soon" (Canon mount available for preorder).
Adorama only has the Sigma mount lens in stock, but at this moment is offering a free Sigma Dock with preorders.