The PA322UHD 32-Inch Professional UltraHD 4K display is here and attached to my 2013 Mac Pro. Setup was flawless; absolutely no configuration or special action required, just plug and go. The PA322UHD runs at all resolutions at 60 Hz, as it ought to.
There are system bugs too (not unique to the PA322UHD). At scaled resolutions, the native resolution is not reported correctly.