This is a strange one. I have actually stumbled across a very odd solution to a problem I actually wasn't aware I was having (in all of my games) until recently. The problem was a subtle game lag. No freezing/stuttering, but gameplay (in this case, Batman Arkham City) was generally slow. My system is HP Pavillion DV6, running Windows 7, Intel i3 processor and Radeon 5650 with switchable graphics. The strange solution I stumbled across was simply watching a video on YouTube!! If I start up a game, then open up Firefox and go to you tube, play any video and then return to the game, the game functions flawlessly and much much faster! I thought this might just be a Batman issue, so I ran Elder Scrolls: Skyrim (which I had already played through with no apparent issues) and went through the same you tube process. When I returned to the game, again it was much much faster than when I played it previously!!
I've obviously stumbled across a solution, but I am still wondering what the hell is going on and why running a video on you tube corrected it! I'm baffled.