How to fix severe frame drops with 4K MOD in Red Dead Redemption 2?

It was unbearable; after enabling the 4K MOD, Saint Denis turned into a slideshow with 15 FPS, which made me furious. I recklessly tried to overclock the VRAM in the driver, which resulted in artifacts and a Blue Screen of Death. I then used the GamePP DLSS/FSR Image Sampling Calibrator to find VRAM bandwidth usage at 98% per GPU-Z, then set render resolution to 85% with DLSS Quality and 80% sharpening. 3DMark showed frames stabilized at 45-55 FPS per RTSS, with AIDA64 temps at 75-81℃.