I shot the Sigma Art 50/1.4 extensively on a Nikon D810 and D850. As others have said, it's still one of the best standard lenses available. There are, however, a couple of things you should know.
First, if you're shooting it on a DSLR, you'll need to buy the dock as well and calibrate the AF. Out of the box it can be a mile out. Which is a pain in the ass! Autofocus is also quite inconsistent, which makes calibration difficult. Really you need to focus them manually using magnified live view, which is a complete ballache since it requires a tripod. So, although the optical design trounces Canikon's f/1.8 and f/1.4 primes, you should bear in mind that it's hard to exploit it. I used the Nikon 50/1.8 G when shooting handheld just for the vastly superior AF performance and lighter weight. On a tripod in liveview, however, the Sigma is supreme.
The other thing you should know is that the Sigma 50/1.4 leaves quite a lot of CA uncorrected (by today's standards). It's extremely sharp even wide open, but specular highlights and highlight edges can look a mess even stopped down.
And the final thing - an announcement from the department for the pigging obvious here! - it's big and heavy. As I say, out for the day and shooting handheld, I left it at home and took the plastic 50/1.8 instead.
