Barely into the 1st mission I had to uninstall the game because I've noticed FPS fluctuating between the low 30s to steady 60s.

Played around with the settings and no change.

My system is a 3770k overclocked to 4.6 GHz running GTX 680 SLI.

Will be avoiding all future Crytek products.

those frames sound like only 1 gpu being utilized. What settings and AA are you using? Driver version?