The one thing I won't ever turn off is DS, personally it is a must have as it makes everything look so much better IMO. I would rather turn MSAA off instead.
Currently I have PD at 1.5 and most (if not all?) settings on High, DS On, MSAA at 2x, Max sliders on Visibility + Trees + Grass/Clutter, AA at 8x, Terrain Shadows at Default. This is all from memory, but I believe it's accurate. I am anywhere between 25-45+ FPS. Mostly 45 with drops down to 25 intermittently.
I'm with ya there :doh: