Image quality, vignetting and distortion test results along with specs/measurements and product images are now available on the Sigma 50mm f/1.4 DG HSM Art Lens
Here are some direct comparisons you might be interested in: Canon EF 50mm f/1.2 L USM LensCanon EF 50mm f/1.4 USM LensCanon EF 50mm f/1.8 Lens
(at f/1.8)Sigma 50mm f/1.4 EX DG HSM Lens
(not the "Art" version)Zeiss Otus 55mm f/1.4 Distagon LensZeiss 50mm f/1.4 Planar T* LensZeiss 50mm f/2.0 Makro-Planar T* ZE Lens
The Nikon 50mm lens results are also available, but they are captured using a Nikon DX3 vs. the Canon EOS 1Ds III. Use your discernment in making these comparisons.