Finally bit the bullet and bought MOOCTS today, and somethings not right. I load up the game, and get 120fps through the intro movies, dropping to around 55fps at the main menu. Once I enter a game, everything drops to 12-16 fps, though. This happens no matter what resolution I am running at, and no matter what graphics settings I set (640x480/Very Low/No AA is the same FPS as 1080p/Ultra/8xAA). The weird thing is, if I exit the game in progress back to the main menu, the FPS does not go back up to what it was when I first started, it stays at 12-16.

Is there something I can do about this? The game is basically unplayable at this point.

SPECS:
Core i7 4770K (stock speeds)
32GB RAM
nVidia GeForce GTX 780 (GeForce Experience says I should be able to run this game fully cranked)
Driver: 376.19 (latest, 12/04/16)
Game is installed onto a Samsung SSD
No weird settings anywhere, this is a stable system in all other games

Found the problem. The GOG Galaxy overlay was causing it; disabling it brought the FPS back up into the 30s on 1080p/ultra/8x.