I'm getting terrible speed drops during scene transitions on my Intel 760P 2TB; do I need to reserve space?

Entering large cities was a nightmare; the loading screen would just hang at 99% for fifteen seconds. The Intel 760P uses QLC NAND, and once the drive is over 80% full, the SLC cache shrinks so much that write speeds plummet from 3000MB/s to under 500MB/s. I tried running a disk defrag, but it only saved about 1 second—totally useless against the physical limitations of QLC. I ended up nuking a bunch of redundant data to force a 20% free space buffer and manually triggered a TRIM optimization. In Resource Monitor, disk active time dropped from a constant 100% to around 40-60%, and city loads went from 25 seconds down to 12. I did notice some other apps launched slower right after clearing space, but a clean driver reinstall fixed that. Temps are stable at 38-45℃ with load at 15-30%. CrystalDiskMark confirms random writes are back to normal. Capacity check complete.