I run on normal windows, and when the flamethrower throws fire, my performance drops to about 25 fps, which is still playable, but annoying. But, i used to use linux, and i've noticed that linux is extremely laggy compared to windows, it isn't really suited for gaming. All i can say, is use proprietary drivers, which i assume you already use. I was thinking it might have something to do with OpenGL on linux and DirectX on windows, but i'm not sure.