I'm seeing huge FPS jumps while walking through mountains in Death Stranding 2 (PC), why is this happening?

Whenever I traverse complex terrain and flick the camera, the frame rate bounces between 50 and 75 FPS, which totally kills the immersion. The XMP config on the Asgard Thor DDR5 6400 has some compatibility quirks on certain boards, causing effective bandwidth to fluctuate between 45GB/s and 52GB/s with uneven latency. I tried turning on Windows Game Mode, but it did nothing against a hardware bandwidth bottleneck, which felt pretty hopeless. I eventually went into the BIOS, switched to XMP Profile 1, and bumped the voltage to 1.38V. In RTSS, the frame time variance shrunk from 18-35ms down to 22-26ms. RAM temps climbed from 48℃ to 56℃, so I had to crank up my intake fans to keep things cool. Now it sits at 52-58℃ with the CPU at 65-71℃. The jumps are gone.