My Intel 760P 1TB reads drop significantly after 3 hours of Dragon's Dogma 2. Should I change the write cache?

I thought this build was solid, but after hitting the complex city areas, my sequential reads slowly bled from 3000 MB/s down to 800 MB/s. The scene loading became a slog. I tried running a disk defrag, which freed up some space but did absolutely nothing for the speed—total frustration. I went into Device Manager and flipped the write cache policy from Auto to Force Flush, and set the power plan to Ultimate Performance. Monitoring showed reads bouncing back to 2200 - 2600 MB/s, and frame times tightened from a messy 25 - 60ms down to 18 - 24ms. Like before, Force Flush caused some weird idle disk activity, which I fixed by disabling the Indexing Service. SSD is stable at 48 - 55℃, controller at 62 - 68℃. Swapping performance modes confirms the speed no longer tanks, and frame times are now locked at 5.1 - 6.4ms.