When it is completely maxed out you should average ~30FPS with decent hardware. Running BF4 on high will get you smoother gameplay.
Overall the 660 is a mid to high end GPU that isn't meant to max out new releases, but rather make them fairly playable (medium-high settings) while maxing out modern games.
I currently have an ASUS OC 660 and it struggles to max out games like Assassins Creed IV with playable fps, so I find myself putting settings to medium to ensure 60fps or high for 45fps.