I get random FPS drops in SP and MP, it doesn't matter the terrain, environment or video settings.
I get decent FPS on Overall High settings and out of nowhere I get some awful FPS drops for 15-20 secs and then they go back up, and this happens very frequently.
I have tried with the lowest video setting and i get same result only with bad visuals.
From what i can tell it's not hardware related since the CPU doesn't get at 100% in one core (the other 3 top at 50-70%), the GPU handles easily the High settings, and the RAM and SSD are enough.

PC specs:
OS: Windows 7 64bit
CPU: AMD FX-4100
GPU: MSi Radeon HD 6850
Ram: 8GB DDR3 @ 1333MHz
Disk: SSD A-DATA XPG SX900