I've actually switched away from the GTX 960 due to laggy graphics and I am using an Asus RX 560 4GB OC, however I was experiencing some random freezing and someone advised me to add this -rad4200 custom flag under the boot options in my config.plist . I thought all was ok today since I added it last night and I hadn't experienced any freezing today however when I stepped away from my monitor and put them to sleep using hot corners, I could not wake them when I returned and had to hard reset the system. Attached is a copy of my config.plist for review if you have a moment. I'd like to keep the 560 as the graphics are very fast and snappy.