Why does FPS crash from 90 to 15 during zombie hordes in Days Gone?

Just as I reached the center of a zombie horde, my frame rate plummeted from 90 to 15 FPS, which was absolutely maddening. I tried disabling XMP in the BIOS to run at default frequencies; while the drops stopped, I lost 20% overall performance, which was unacceptable. I used the GamePP BIOS Load-Line Voltage Guide to increase memory voltage from 1.2V to 1.32V per HWiNFO and loosened the tRFC parameter. The minimum FPS rose from 15 to 52 per RTSS monitoring, and MemTest86 confirmed zero errors over three cycles, while temps stayed at 48-54℃ per HWiNFO.