New Admin still had the issue, and System File Checker found nothing.
Looking back to the thread I linked, someone else specifically mentioned theirs was a GPU issue instead of memory issue here, and there’s a similar issue here. This leads me to believe some other mentions are speaking of a GPU spike instead of just a memory leak.
I strongly believe this is on WoW’s side, not my PC. I will reinstall Windows if you believe it absolutely necessary to try, but I’m definitely not paying someone to look at my PC when it’s only occurred while playing WoW with that specific setting, and only since 8.3 launched.