I matched the Sigma 50mm f1.4 Art against the Canon EF 50mm f1.4 prime lens and was surprised by my anecdotal findings. The older, much less expensive Canon EF 50mm seemed to hold its own against the much more expensive Sigma prime 50mm.

 Based on what I see, I can't recommend upgrading or buying the more expensive Sigma prime, unless the copy I used needed some micro-adjustments via the USB dock. I'm going to reach out to Sigma to see if they will send me another copy and if they do, I'll re-check the lens against the Canon 50mm f1.4.