Added to my review of the Sigma 35mm f/1.4 DG HSM is a 3rd field comparison of the Sigma 35/1.4 versus the Canon 35/1.4L.
Large images and generous crops from f/1.4 - f/5.6. (too dark for f/8!) The subject in this comparison is planar in nature, showing some behavioral differences with respect to the nominal plane of focus.
Why so many comparisons? My working theory is that the Sigma 35/1.4 DG HSM is a superior lens to the Canon 35/1.4L in every situation. So far that theory holds. Were it not for my particular situation (this site), I’d be thinking hard about disposing of the Canon lens (and I probably will at some point). That said, the Sigma 35/1.4 DG HSM has yet to prove itself as a long term reliable lens, so I don’t advise pro shooters or Treebeard to be hasty.