I shouldn't be lagging on ultra with these specs...but i do..why?
Single Radeon 6850 oveclocked to max useing AMD overdrive
8GB DDR3 dual channel memory
AMD Athlon II x4 640 Overclocked @ 3.6GHz
What makes you assume you shouldn't be lagging?
Unfortunately your system isn't strong enough to play BF3 on ultra. BF3 is very demanding.
Try lowering your settings slightly until you get decent FPS. A good place to start will be lowering AA and shadows and turning things such as HBAO and SSAO off.