Why does Need for Speed drop to 40 FPS in city areas?

The initial smoothness vanished as city complexity increased, leaving me feeling helpless against erratic frame drops. I tried enabling Game Mode and disabling all startup items, but the drops persisted, making the effort feel futile. I then used the GamePP BIOS Load-Line Voltage Guide to loosen timings to 38-38-38-80 and bumped voltage from 1.35V to 1.38V per HWiNFO. AIDA64 stress tests showed zero errors, latency stayed at 92-105ns via AIDA64, and temps hit 54-60℃ per HWiNFO.