Why does Cities: Skylines II stutter during rush hour on ASUS B650M?

Rush hour traffic in Cities: Skylines II was stuttering badly, ruining the sim. I tried enabling XMP in BIOS, but it blue-screened on boot. I used GamePP BIOS Load Line Voltage Adjustment Wizard to raise memory voltage from 1.35V to 1.40V. MemTest86 showed bandwidth jumping from 45GB/s to 55GB/s. GamePP sensors kept RAM at 48-55℃. The city runs smooth now, so I can switch to the next project.