chances are its a hdd problem. if its 7200 rpm its likely your not getting the textures fast enough. if you have another identical drive try raid 0.
neither parts are classically bottlenecking as far as gpu and cpu go as neither are hitting 100%.
try using the bf3 configuration and limiting your fps to 60 this should stop the fps droop and smooth out the stutter if there is any.
also try using an fxaa injector. it doesnt just work with nvidia cards and doesnt have a high overhead that comes with fsaa.
switch to hbao rather than ssao it looks better and has a lower overhead.
you should now be able to run aa without impacting the fps to much if you dont bother with the injector.
I'm running BF3 max with a 7200RPM drive, and no fps drops...