Why does MGSV FPS drop from 120 to 60 in HD mode?

I was so excited for the HD graphics, but in complex base scenes, the FPS dropped from 120 to 60, which was a total mood-killer. I first tried overclocking via the driver; while it gained 5 FPS, it introduced screen flickering, a compromise that was far from perfect. I used the GamePP DLSS/FSR Image Sampling Calibrator to adjust the sampling rate to 85% and boosted sharpening. Frame times quickly converged to 8-12ms per RTSS, and GPU temps stayed at 62-68℃ per HWiNFO. The visuals are now buttery smooth.