radeon 6870 matched with your cpu doesnt make it any more than low end system. and looking at the pictures everybody can see that you dont really know how to get the best fps or pic out of your system. and that is what's holding you back.
semp
the guys got a point, at least about the hardware. A core2duo may not be as obsolete as a single core processor, but its still old. Like 4-5 yrs old to be exact. Your GPU is only gonna be as strong as your weakest component, and in this case it is your core2duo by a decent margin. regardless, if you turn down your eye candy a core2duo should be able to pull at least respectable frame rates out of this game.
EDIT: to answer the question you just posted, turn down anything having to do with textures. When you are having FPS drop due to a processor bottleneck you get the most return out of lowering settings that impact the amount of textures/polygons on your screen.
semp, I dont have frame rate issues in game (steady 119 to 120fps at my current settings), but I do have minor microstutter issues when in a large furball running a TrakIR. I'mf pretty savvy when it comes to hardware, but if thats something you have any suggestions on I'm all ears. Have you ever experienced this even though you may have high frame rates?