I was experiencing significant lag issues in various Black Ops servers, and tried a variety of solutions and combinations; this lousy lag existed for the first 1-2 minutes in quite a number of servers and games (Multiplayer) in Black Ops before I changed a setting; I tried a variety of updates to drivers (not just video, but bios, HD, turning off a, b, c, or combinations of background software; I've spent almost a month playing around; none of the solutions given by people in this or other messageboards worked (I didn't emply some that would mess with 2 video card set ups). Meanwhile, some servers were fine in gameplay, with no video studdering or lag issues; it wasn't v-sync either; with it off, gameplay was pretty lousy; pings were from 45-100, depending on server, and it wasn't the change in pings that contributed to problematic video.
I have 2 x 6870s in Crossfire, win7 64bit, 6 gig ram on an Asus P58, with an Intel i7 930 2.8mhz chip.
The solution, with running max settings, w/out running AA, is go to in-game settings/graphics/texure filtering, select bilinear; mine was set to triple or trilinear.
My gaming improved actually, and was able to react quicker in mad-fast game play (Nuketown dem or dom).
Hope this helps you;