I'd turn that, HDR, shadow and reflection settings off too. Also, there must be an fps setting that allows you to cap maximum fps. If you haven't done it so far, cap that at 60.
No other solution comes to my mind. Except maybe, if you don't mind having some insanely amusing textures, you could try the Scary mod. It will whack the graphical beauty of the game off, but give you fps in return.