Shortly after the launch of AMD's Radeon Software Crimson Edition, reports hit the web about a fan speed bug that could cause cards to overheat. That one has been fixed, but now AMD confirms there's also an issue with downclocking and stuttering in games. AMD is working on a fix and recommends rolling back to Catalyst 15.11.1 Beta or 15.7.1 WHQL if you're experiencing this problem.
@noirgheos@AMDGaming We're aware & investigating the issue. It can be resolved by rolling back to Catalyst 15.11.1 Beta or 15.7.1 WHQL. ^MB