Why does Nightingale FPS drop from 75 to 40 when building?

While building a grand manor, my frames plummeted from 75 to 40 per RTSS during camera rotations, which ruined my flow. I first tried lowering the maximum processor state to 99% in Windows; it dropped temps by 5℃ but caused severe performance loss and even more frequent stutters. I then used the GamePP Fan Curve Configuration Panel to set a 65℃ speed surge point with stepped acceleration. Now, HWMonitor shows temps stabilized at 72-78℃ and CPU-Z confirms a steady 4.2-4.5GHz clock speed.