I've asked in numerous forums so far and haven't found a fix for my issue. My R9 270 (1024SP) from PowerColor is dropping it's core clock speeds. I don't believe it's a thermal issue as MSI Afterburner is reporting max temps around 65-70 degrees.
In CS:GO my frames drop from around 300 to 60 and in LoL from 144 to 15-30.
I've tried updating drivers, using old drivers, DDU+Uninstall, Uninstalling all GPU management software (MSI Afterburner, etc.) and it still happens.