Look up the specs for the processor in your system, then chart the temps alongside per-core clocks.

On Intel chips with a 1 to 4 core boost, no cores will rise above the base clock when thermally throttled, voltage may increase, and frequencies will be lower. You can run a CPU bound benchmark until temps rise and note when the performance begins to decrease.

On desktop Intel processors, this usually happens between 70-80°C.

That should work for revealing throttling -- you will see that it tops out at 1.1 GHz or something.