A 15 year old, first generation Sigma 70-200/2.8, wide open on a K3. That's only 24MPx, but on an APC sensor it has a pixel density equal to 54MPx full frame. I really wonder what people do with all this sharpness they apparently need.
How does it look up close when it's blown up to 60x40"?
Also, how does it do in the corners when shooting a landscape, where everything is in focus and you need corner-to-corner sharpness? A portrait where most of the image is out of focus is hardly a useful test of lens sharpness. And how does it handle CA and purple fringing when dealing with high-contrast edges or bright highlights?