I am running a 14 mb save clocking in at about 265 hours and I'm starting to get lag during my gameplay. Every couple minutes or so the screen seems to skip a bit and some of the sounds don't sync with my actions.

The lag also continuously gets worse as I play, until I encounter extreme skipping and/or the game freezes on a loading screen.

Are there any suggestions that would help me? I would like to have smooth gameplay for Dawnguard, but purchasing it would go off the table if I couldn't use my character. Is this problem indicative of the new patch, or the size of my save file? Can I reduce the size of my save file? What about clearing the system cache? Would that help and how would I do it?