Why does my CPU clock drop to 3.0GHz in Bohemian towns?

I was so excited to run through Bohemian forests, but then my CPU shot from 62℃ to 88℃ per AIDA64, and the game stuttered. I tried the Windows High Performance power plan, but that just pushed temps to 95℃ and made the stuttering worse, which was incredibly discouraging. I used the GamePP Fan Curve Configuration Panel to set a linear growth of 1600-2100 RPM for the 70-85℃ interval. HWMonitor showed peak temps held at 81-85℃ per AIDA64, and frequency fluctuations narrowed to 0.2GHz per CPU-Z.