I'd say you could maybe get away with current processor but GPU and RAM upgrades are necessary.
Have you done clean up and repair and/or renaming Saved Games folder to rule out problems with install causing performance issues?
As far as settings, yes mirrors do have a big impact. Since you don't have much RAM you should have preload radius all the way down, shadows and water on lower settings, DOF and Lens Flare off, view distance and trees on lower settings.