I have a Samsung 4k monitor hooked up to an Nvidia Geforce 760 in my Hackintosh via DisplayPort.
If I leave the settings on 'Best for display', for some reason it goes into 1080p mode.
If I put it in 3840x2160 resolution manually (which, for some reason I can only do using the screenresx third party app, the resolution isn't listed in the normal display settings), everything is absolutely tiny (buttons, menus etc).
I had thought (and have seen screenshots) that there would be the ability to change the scaling of all the items within Yosemite, but the only way I can make everything readable (and even clickable without pico-adjustments of the mouse!) is by downgrading the resolution, which seems a bit pointless.
Has anyone got 4k working as I was expecting, or have any suggestions that I could try to get this functionality somehow?