sys specs: AMD phenom9750 quad core 2.4, 8gb RAM, AMD HD 7700 core graphics card.

The game runs very well on my system even on high. (with the blur effect and post processing turned down) when not a lot of enemies are around.

But when I play with many people in single player or multiplayer the game drops to an unplayable frame rate- I'm talking 5-10fps.

This is big problem, cause I have above the recommended system specs.
No other game I own drops in performance like this.