Could elaborate please? Noob here. I know how to backup and flash via ATI Flash/Polaris Editor but don't know Ubermix.
So you know the basics, use backuped bios in Polaris and cope Uber-Mix timmings in 1750 and 2000.
http://www.overclock.net/t/1604567/polaris-bios-editing-rx5xx-rx4xxGo here -> first post -> performance timings -> uber-mix 3.1
If you get lot of memory error try lower clocks it should go somewhere to 2100MHz but there is almost no difference between 2000MHz and 2100MHz with this timing...
If it didn't work you need not so agressive timings. In that thread is Uber-Mix 3.2 you have to find it.