Just tried updating the Nvidia driver to latest version and it locked the refresh rate to 30Hz in this pre November version.
I rolled back the driver to 353.62 !
So now I will update Win10 to 1511 and then install the 353.62 legacy driver and see if this works.
OK this is fixed ! You have to run NVidia driver 353.62 ! This allows me to run at 3840 x 2160 and I get 60Hz. Obviously later drivers do not work correctly in Windows 10.
I found other people with same problem and this has fixed it.
While it is a bit late to try, you could have used the customize option, preserved your native resolution, and up'd the refresh rate to 60. Windows may not have taken a liking to this, but there is a small chance it would have worked.
I assume you mean the 'customise' option in the NVidia control panel ! Tried that, did not work. Tried everything that people suggested without any success. This is the only way I could get 3840 x 2160 60Hz.