If you were lagging and your FPS and bandwidth are both good and everyone else is lagging. It is most likely an underspecced server. Don't keep playing on the server, just move to another.
Also, the ingame browser for doom3 is FSCKING TERRIBLE. Dunno who thought that abortion up, but use All Seeing Eye if you are trying to play online. With the ingame browser I could not find a single server that I pinged 60 to that would let me in. So I loaded up all seeing eye and found TONS that I pinged >50 to, that had tons of people and would let me in.
FYI: 
For Singleplayer I use 1024/High
For Multiplayer I use 800/Low. And still tweaking. The more FPS the better in multiplayer...