I have a few friends that have a similar set up. They turned off shadows and their fps stays strong now.
I run my system on a 47" LED LCD tv at 1920 x 1080 res and my fps is usually 70+ but during heavy populated areas with tons of explosions it drops down to 50s. Last night on the imperial fleet my fps plummeted down to 30s.. it was packed LOL.
My system is as follows:
amd phenom II X4 955 Black Edition Deneb 3.2GHz
6850 radeon
8gb of g.skill sniper ram
500gb 7200 rpm HDD
OS: Win 7 Ultimate
I never have lag, no graphical issues. The only thing that drives me crazy is the loading screen takes forever, but everyone I know has this same issue. Some have SSD and some have HDD.
Good Luck