In many single player scenarios, the game performance drops to very uncomfortable frame rates even if you have more than sufficient GPU. The reason of this is that most of the computational overhead is produced probably by the presence of many game entities, such as vehicles, soldiers, etc... and the way their AI and simulation is being handled.

When playing combined arms mission, no matter if i set very low or very high graphics settings, the framerate almost doesn't change. My CPU (i7 2600k) should be also more than capable to handle the computations, so there is probably something being done extremely inefficiently.