After some research I managed to fix it and configure 4k 60hz on hd7850 with CAC-2070, So for anyone following this – the fix will probably work on any GCN card, like hd7970, r9 290x, r9 390, etc.
So it turned out that AMD removed the driver support for the Active Adapter (DisplayPort to HDMI2) when they released Adrenalin, so basically the last version that supports 4k 60hz via Active Adapter (DP to HDMI2) is Radeon Software Crimson Edition 16.8.3, basically all you have to do is uninstall adrenalin driver, and simply install Crimson 16.8.3 instead.
you can download Crimson from AMD’s website: https://www.amd.com/en/support/kb/release-notes/rn-rad-win-16-8-3
- Don’t forget to uncheck the box that automatically updates the driver
Club3d support – if you’re reading this – your description in CAC-2070 page is misleading, please specify that 4k 60hz will only work with Crimson 16.8.3 driver when using GCN cards.