I keep looking but have never found this anywhere. It seems like an obvious thing to be curious about yet dead silence in the review-o-sphere.
So many reviews of Sigma lenses find erratic focusing to be an issue.
Sheer guess-ery is rampant in forums, when people attribute this erratic behavior to either 1.) bad quality control/design, or conversely, 2.) software problems due to difficulty rigging something so 3rd party lenses autofocus on Canon (or Nikon) bodies. A test to prove which (if either) of these is the culprit would be read with interest by lots of people with major brand camera bodies trying to decide whether to buy into the love-fest and pick up a Sigma Art lens.
Obviously the review would be of more interest if the Sigma lens tested were the much talked-about 35 Art or 50 Art rather than "lesser" Sigma models.