The aesthetics of this feature are great, however the blow it gives my performance makes it unusable. I am using a Dell P2715Q 27" 4K display, 16GB Corsair RAM, 120GB Crucial SSD as boot and scratch disc, and XFX R7 250X GPU; all in Windows 7. I was running PS CS5, but decided to do a trial run with PS CC 2014 due to the ridiculously small UI in CS5 at 4K resolution... The performance slow down from CS5 to CC 2014 is ridiculous with the 200% UI enabled, and disappointing even without it. My actions that run lightning fast on CS5 take a significant amount of time in CC 2014. All in all, I will be reinstalling my CS5, and reducing my resolution to standard high definition again... unfortunate that my brand new screen has to be held back to half of it's capabilities due to poor development on Adobe's part.
Note: This conversation was created from a reply on: Photoshop: Introducing scale the UI 200% for high-density displays for Windows.