[Huge lag spikes]

Same here, I think. Played the game for a week at a fairly solid 60fps (with rare bumps when things got busy) and then suddenly, it chugs and surges or goes into a slow-mo lag mode. Every time. No settings were changed, latest drivers (but tested old ones just in case,) I defrag regularly, tried optimizing the cache, deleted and reinstalled, checked for malware, tested hardware, etc. etc.

The problem seems to stem from the game loading things in, but nothing changes no matter what settings I use, which makes sense, because the game ran almost flawlessly for over a week on my crappy little OEM GTX 645. 

Win 7 Pro
i7 4770
12GB DDR3
GeForce GTX 645