If you quit and restart immediately when the performance drops, do you get another 5-10 minutes of normal performance, or is it less?
Is there any additional drop in performance over time?
A few people have slightly underclocked their video cards (
MSI Afterburner) to avoid DirectX 'device removed' errors (
topic), as well (one person recommending to lower the Core Clock and Memory Clock options by around 100 for that issue).
Make sure the Virtual Memory setting in Windows is set to automatic / system managed, rather than being disabled or set to a fixed size. To check or change virtual memory settings:
Win 7/8 or
Win 10.
