Wheever i play games like red faction guerilla or fallout 3 my computer starts to lag after the heat gets really high, like around 109 C. My computer is a g50v with a NVIDIA GeForce 9800 GS.
I've noticed that NVIDIA mobile gpus get really hot. I had a dell 1420 with 8400m gs and that thing ran hot. Idle temps were around 60c. playing games it reaches up to 90 to 100c. i cleaned the vents once in a while since it was easy to clean them on this laptop. A notebook cooler helps too. That laptop was replaced by a studio with ATI graphics. This thing runs very cool compared to the nvidias. 60c on ati was when it was under heavy load.