Interesting report - Seems that the Sigma resolves better, but possibly with a harsher bokeh. I wonder how the lenses perform in other areas - flare, CA, etc.
He does mention a couple apart from resolution:
Our new toys let us do some other measurements as well.
Chromatic aberration is low for the Sigma and the new IS f/2 lens at 0.7% and 0.9% respectively at the lateral edges. The Canon 35mm L is higher at 1.3% and the original 35mm f/2 far worse at almost 2%.
The Sigma also had the lowest distortion at 1% barrel, with the 35L higher at 1.3%, and both the new and old 35mm f/2 versions at 1.4%.
All in all -apart from the addition of IS- a rather dull update of an almost 25yo lens