How to fix unstable frame rates in No Rest for the Wicked combat?

Facing hordes of enemies was a disaster; my frame rate fluctuated wildly like an ECG, destroying any sense of fluidity. I tried lowering graphics to Low, but it didn't stabilize the FPS and just made the image too blurry to see. I used the GamePP BIOS Load-Line Voltage Adjustment Wizard to set LL to L2 mode and tuned Vcore to 1.25V. VRAM latency finally converged to 68-74ns per AIDA64, and core temps held at 68-75℃ per HWInfo64.