looking at your rig, its no wonder you love this demo so much. Its about time for a good western.
my computer has 15 processes and the specs in my sig, on 1024 X 768 one the first level I average about 35 fps with most settings on low and SM 2.0.
One the second level with the huge outdoor environment I got as low as 12 fps on 1024 X 768 and mostly low settings. Even at those settings its the best looking game I think I've ever played.
Very demanding, but very cool game.
At 1280 X 1024 on medium/high settings, a 7800gtx will go as low as 20 fps, this game is just beautiful & demanding so if you got a nice video card its a must have.