To add to your post, all modern CPU's will throttle when their thermal design power is reached. It is done to save the cpu from burning up. So it slows down a lot to until it cools down enough to resume normal operation. The job of the thermal paste is to transfer the heat generated by the cpu to the heat sink where it dissipates. Without paste, the transfer of heat is compromised because there are micro gaps between the surface of the cpu and the surface of the heatsink. The thermal paste's job is to fill in these gaps, thus allowing proper heat transfer. Over time, this paste becomes brittle and dry, and the heat transfer is no longer as efficient, causing the cpu to potentially overheat and throttle. So if you have a game that kind of "stutters" this might be the reason why. As a general part of my machine's clean up and preparation, I always remove the heatsink from the cpu and clean out the old paste so that both surfaces are shinny and devoid of any of the old paste and the put a nice layer of new paste and re-assemble.