So here we go again.
Last time I had a similar problem, installing the latest driver (17.5.2 at that time) fixed it.
After almost a year, last week I resubscribed to and reinstalled World of Warcraft.
That driver gave me horrendous fps spikes and stuttering in various parts of the game.
Installing 17.8.1 brought back the flickering I experienced before (Second screen flicker with minimal OC with new drivers ) so I rolled back to 17.7.2.
With 17.7.2, WoW was fine, but the gpu boost function never turned on, no matter the load or game i.e. core clock was stuck at 950mhz. I reset the custom settings at MSI Afterburner (AB), restarted - the same. I removed AB - the same. Reset all user options at the Radeon client then restarted the computer for the nth time - now it boosts to the factory default of 1070mhz (Sapphire Vapor-X (dual-x) 280X), but the moment I alt-tab out of a game or a fullscreen app, the core and memory clock gets stuck at 300/150, which causes even greater flickering on both my screens now.
Main components: Gigabyte B75M-HD3, Chieftec CTG-500-80P, 2x4GB Corsair Vengeance 1600mhz CL9-9-9-24 ram sticks, the aforementioned video card and the latest stable build of Windows 10 Pro (15063).