I have been at this for hours and hours and its frustrating me very much.
I recently purchased a 4k monitor and was unable to achieve 60hz on HDMI, then I learnt I needed to use DisplayPort to Mini Display port. So I purchased a DP > MiniDP cable and I am now using it, though I'm getting the same results as HDMI (4k @ 30hz)
When using bootcamp, 4K @ 60hz is achieved and its PERFECT, but just on MacOS Mojave I can't get past 30! Any thoughts would be appreciated.