I'd be interested if I didn't already own the 50 Art. I've seen exactly what you describe. By all accounts, this is an amazingly sharp lens, among the sharpest out there.

I have had very good luck with my Sigmas. There are those that complain about focus. If you get it, do buy the docking station and take the time to calibrate the focus at different distances. This was not so much a problem on my 50A and is not a problem on my 150-600S, but my 35A (since sold) had this mid range (~10 ft) where it struggled until I did the calibration with the docking station.

But, with all seriousness. Go for it. Sigma is doing some great work with lenses. My next most coveted lenses are both Sigmas, the 14A (which I am renting for the second time) and the 135A.