Price is good, sharpness looks good on the various 5Ds samples out there, longitudinal CA looks well controlled...
Probably not as sharp as the Art lens, but should hang with the rest and adds IS and potentially fast AF.
The 85/1.8 USM is the standard here, though- if it's that fast, that would be awesome.
Canon 6D|24-105/4L |70-300/4-5.6 IS USM|50/1.4 USM|50/2.5 CM|50/1.8 STM|85/1.8 USM|Samyang/Bower 14/2.8|24/2.8 IS|Sigma 150-600 | C
Canon EOS-M|11-22 IS|22/2|EF-M 18-55