You can set
max_fps 100
To get 100 fps. That's as high as CS will run though.
It really depends on your settings though. I ran it at 1280x1024 on my GF2 GTS and it was pegging off of 100 almost constant (long open areas with people and smoke made it drop down to 30). On the other hand, my new R9800 Pro can sit at 50 fps if I have truform, 16x aniso, 4x quality FSAA, etc etc etc on.
What I would do in your situation is go for 8x aniso, 2x FSAA and run 1280x960. That should give you decent solid framerates and quality.