Theres a config out there that reduces the graphics settings as far as they can go I think. Gives you probably the best fps youll get, but makes it look like absolute shite imo, but I guess your willing to sacrifice looks for speed, whereas im the opposite.
Turn down the res, and as wolf said, turn the vid options to minimum.
Actually I highly reccomend turning off water reflection to anyone who isnt running a top-notch pc. The water still looks great, and it makes a huge difference when theres water on screen.
Of course, the ideal solution is to upgrade your PC
there is a console command but i dont think it makes any difference, well i dont know, it might: fps_max 300 is default, and u can change it Eg. fps_max 600.