I have a 4K Philips monitor (BDM4065UC 40", 4k) and bought a Sapphire RX 470 this week.
Without any driver i am at 64 Hz at Ultra HD (3840*2160)
After installing 16.9.2 (or 16.9.3 beta) i only have 30 Hz at that resolution.
It is not a matter of the cable (high quality DP cable). I had a Geforce 980 Ti before and there were no problems. Even with the Intel CPU graphics i had 60 Hz at ultra hd.
This seems to be a driver problem?
How can i solve this?