Xitek published the first comparison images of the new Sigma 50mm f/1.4 DG HSM Art lens and three other lenses (click for larger view):
The nomenclature of the jpg files shown is as followed:
Vignetting graphs and specs comparisons between the four lenses:
Sigma already said that the performance of their new 50mm Art lens should be very close to the $4,000 Zeiss 55mm f/1.4 Otus Distagon T*.