I have got a UP2715K display from Dell and a PNY Quadro M2000. Unluckily I'm not able to achieve a 5K resolution on Windows 10 Pro, even if all the drivers are installed (and both the DP cables are connected).
I've already checked both the cables and both works fine. Surfing the menus, I saw that in the NVidia control panel only one cable is detected, in the first DP connector.
So I did try to unplug the 2nd cable, and the computer didn't even notice it. I did try to install other drivers version too but without success. NVidia control panel (sorry for the Italian language)