wolfiZ

Are you watching your HD light during those lag frames? I bet it's the HD texture packs, regardless of your vid memory/gpu speed. I mention that because I have 2gb vid mem (not sli) and had identical lag as in your vid. My solution, sice I didn't want to remove my HD textures..was to half scale the largest *_n.dds textures ONLY (I searched my texture folder for _n.dds and sorted by size), with Optimizer Textures (Ordenador.exe). It took a little while, since I had to move the _n textures for each folder to a subfolder to batch process them and then copied them back to their original folders. Lag was gone, and the detail loss, since the main dds's were still unchanged, really barely noticeable. Smooth as silk now. If it were me, I would disable to two texture packs and test for the lag you have again. If it's reduced or gone, that might be the issue. Also, while on the subject; with your HD texs enabled, go to console and type tscr and see if the lag is still there. If it ISN'T, then script lag is affecting frame rate. I've had this issue before too, something to do with the script buffers affecting texture allocation in cpu memory. There are ways to "smooth out" script lag without your game getting borked, since the lag is stored in save games, and if not corrected, can caused frequent CTD in all sorts of situations, progressively getting worse and worse unless corrected..