Also a recent TF2 update brought us this command:
- Added experimental cpu_frequency_monitoring convar to detect thermal throttling. If you have TF2 performance problems on Windows, add "+cpu_frequency_monitoring 2" to the TF2 command line to see if CPU thermal throttling is an issue. If the displayed CPU frequency percentage drops below about 80-85% then you may have a problem with your CPU slowing down due to overheating. If it drops below 50-55% then you may have a serious problem. CPU overheating can be caused by overclocking, insufficient cooling, insufficient airflow, failing or dirty fans, or other causes. The CPU frequency results are displayed with cl_showfps or net_graph. For more detail see https://support.steampowered.com/kb_...2715-YIPD-6873
So this will verify that your CPU isn't downclocking!