Image quality test results have been added to the Sigma 40mm f/1.4 DG HSM Art Lens page.
This is a very impressive-performing lens.
Here are some starter-comparisons:
Sigma 40mm f/1.4 Art Lens compared to Canon EF 35mm f/1.4L II Lens
Sigma 40mm f/1.4 Art Lens compared to Canon RF 50mm F1.2 L Lens (different comeras being compared)
Sigma 40mm f/1.4 Art Lens compared to Nikon 35mm f/1.4G AF-S Lens
Sigma 40mm f/1.4 compared to 50mm f/1.4 Art Lens
Sigma 40mm f/1.4 compared to 35mm f/1.4 Art Lens
Sigma 40mm f/1.4 compared to 50mm f/1.4 Art Lens
Sigma 40mm f/1.4 Art Lens compared to Tamron 45mm f/1.8 VC Lens
The Sigma 40mm f/1.4 DG HSM Art Lens is in stock at B&H | Amazon | Adorama | WEX
Rent the Sigma 40mm f/1.4 DG HSM Art Lens from Lensrentals.