Actually i have the same problems.
My setup is quite good:
AMD 955 4x, 12 Gb Ram, 120 GB SSD ( OS ) and fast HDD, 2x ati 6950 ( running crossfire ), internetspeed is 35/4 ( im streaming c-rpg right now ).
The problem is, especially seen on DTV, the ingame FPS going down badly. Most time, it runs with 120 fps. But when, for excample, there is a shield wall and masses of dead enemies, fps going down to 30. And it seems like there are some "ingame" areas on the map where fps dropping down, im not sure. When this happened, i checked my ping pressing tabulator and its still fine ( 20-29 ). I already changed my videooptions ingame, but didnt really help. So im thinking its not a problem of my hardware or the server, its a problem of the game engine and/or map???
Any advices which would help?