Here are some cvars that should help get it running better, you can then tweak to your liking instead of just using "low quality" in the menu settings:-
Code:
image_downSize "1"
image_downSizeBump "1"
image_downSizeBumpLimit "512"
image_downSizeLimit "512"
image_downSizeSpecular "1"
image_downSizeSpecularLimit "512"
image_filter "GL_LINEAR"
image_ignoreHighQuality "1"
image_anisotropy "0"
image_roundDown "1"
image_useAllFormats "1"
image_useCache "1"
image_useCompression "2"
image_useNormalCompression "2"
image_useNormalCompressionLoadDDSForPal "1"
image_useOfflineCompression "1"
r_multiSamples "0"
r_swapinterval "0"
You use these in a CFG file when running the game. You may need to use "vid_restart" in the console when applying them for the first time. There's a few more you can use to get even better performance out of the game(s).
Good luck.