I have a (pretty old now) Radeon 4870 which I'm using in my windows 8 box. Its using the WDDM (1.1) drivers.
When I have a full screen app open on my primary monitor anything running on the secondary display lags badly. For example I cant play a game on my primary and watch a video on my secondary monitor. When running a non-fullscreen app on my primary there is no issue with my secondary.
Has anyone else had similar issues with WDDM/windows 8? Is this something that will be fixed by a graphics card upgrade?