This started happening in my previous Linux. (Which is my main OS FOR NOW...)
I used to get never below 100fps, usually in 200's or 300's area... Then some day after I took the card out to clean it then put it back in, it struggles to get 30fps, or even 20 fps!
I updated my Drivers and switched RAM slots, I got about 10FPS more.
I got optifine and set it to multi-core loading, increased FPS slightly.
I switched Operating Systems multible times -
Linux Mint 14
Linux Lite 1.0.4
Attempted ArchLinux... (Oh god..)
My current OS is ZorinOS which is a linux Distro which a nice feel and I selected Windows 7 theme so I can move around easier.
Why would it some day go 300FPS then drop to 20... This isn't a lag spike since I never get above 40... It's 40 max and 2 minimum...