I have similar issues and have figured out some details.
The Cpu-usage of "ntoskml.exe!WheaAttemptPhysicalPageOffline+0x350" goes up when i move Firefox to my second screen (~1-2%). When i start a video on youtube (HTML5) the usage goes up again (~20%). When i move the window with the video to my first screen the usage goes down to ~0.1% even while playing a video. With flash the usage is higher but its the same thing with the second screen.
I have a i5-3210M with the graphics driver 15.33.32.64.4061.