your pc should be able to run full speed without getting hot. This is a hardware problem, not a game problem, the game may be taxing the system but it should be able to handle it. Check your fans, blow out the dust, reseal the CPU with new compound if its more than 2-3 years old. Make sure it has airflow. If that isn't cutting it, move the components around a bit can help: make sure the power supply is away from the graphics card, for example. A bigger case is not too expensive, or if you have room, take the power out of the case and sit it on top or to the side can give you better airflow and remove a major heat source.