DxOMark published their test results for the Sigma 50mm f/1.4 DG HSM Art lens for Nikon F mount ($949):
“As one of the key models in Sigma’s new range of high-speed premium Art-series models, the Sigma 50mm F1.4 DG HSM A is notable for high sharpness and control of aberrations, particularly at wide apertures. While it is all too easy to dismiss the Nikkor for its rather low sharpness (particularly at wider apertures), and the Zeiss for its price (with an optical performance that rarely comes cheaply), the Sigma 50mm F1.4 DG HSM A Nikon-mount version is a highly desirable alternative to the more esoteric models available.”