Well, this is a problem with the game, the SF levels are very laggy even with the best equipment. All I can suggest is type flush in counsol once you have been playingn a while. Also try to get a Memory cleaner that will clean up your ram.
go to tweaktown and get the aa tweaks, there is a tweak to increase the amount of vid ram used 4 textures. if u have more than 64 megs of vid ram u will want to change the default'32' to aprox 1/3 of total vid ram, this may help speed up the game.theres just sooo much detail to draw + lots of players
ok so what should i do as i lag like mad also on these maps...
type flush into console, close all background programs, and overclock video card to the most.
try jioning servers w less players ,look for low ping servers , u will get better conection