I've had a go of Killing Floor through the Linux Steam beta client, but performance is pretty poor. My set-up:

Kubuntu 12.10 64-bit
AMD Catalyst 12.11 beta (fglrx)

AMD Phenom II X4 965 @3.4 GHz
8GB DDR3 (1333MHz)

I've just been playing solo. It says I'm getting around 25-40fps, but it lags a lot and as such feels a lot less. Turning the settings down makes a difference but not much. As such it's barely playable. When I play in Win 7 it never drops below 75 fps with v-sync enabled.

Presumably it's a graphics driver issue?

Any tips or suggestions?