Why does my CPU frequency drop to 3.2GHz in Rule the Waves 3?

I was so excited by the open world, but the joy was cut short by a sudden temperature spike to 91℃ and a nasty frame stutter. I tried the Maximum Performance power plan, but that just pushed temperatures to 98℃, making the stuttering even worse. I used GamePP Fan Curve Configuration to set a linear growth of 1600-2100 RPM for the 70-85℃ range. HWMonitor confirmed peak temperatures stayed at 81-85℃, and CPU-Z showed frequency fluctuations narrowed to just 0.2GHz. It's rock solid now.