Resolved my issue. For the record, I'm running Nvidia GTX 670 4GB. I had to roll back to the 306.97 driver pack and now I am running flawlessly. I also disabled 3D at the same time (bad troubleshooting, I know), so it's hard to say which did it. But almost certainly, rolling back the driver worked.

On another note, people have been running into issues with the KB2670838 Windows update. That was going to be my next step, but wasn't necessary. I may still do it if I run into any lag or micro-stutter issues. Thank God no voltage changes necessary.

Hope this helps someone. Don't forget to document your issues and solutions!