I currently have the Asus 27" 3d 120hz monitor, and have the msi 660ti gtx pe oc to 1100mhz, max setting 3d 1080p getting about 60-70fps, wonder if i go with 670 gtx or a 3gb version of 660ti will it be improve my fps?
It's going to depend on the games. It is very unusual for any game to go beyond 60 FPS in 3D Vision, unless you have that 144hz monitor. 3D Vision requires v-sync to function, though Metro 2033 has an unusual way of handling it, which allows for higher FPS, though FPS beyond 60 are just dis-guarded.
If you are getting 60 FPS in 3D Vision, there is absolutely no reason to have more power.