... firstly the games graphics rate is capped at 30 fps, regardless of any other settings, and anyone with a card that has at least 256mb of onboard ram shouldnt have to turn the graphics down in any case, also, if you have at least 1gb of ram then there shouldnt be any slowdown due to the game - assuming you have a processor of at least 2ghz anyway, since most people have spec's that are way ahead of this, then graphic slowdown shouldnt be a problem, unless of course, the slowdown is serverside, which most of the time, it certainly is.
if you are having problems, then there are ways to tweak the serverside issues, to a degree at least.
in the options, under graphics, see how far your viewing distance is set for the different terrain models. realistically, if you have a dsl link of at least 1mb then that shouldnt be an issue, but it does cut down on serverside workload.
i dont really recommend cutting the viewing distances to less than 50 percent though, if your in a city during a live event, then 25 percent might be your best friend :D