I have the AA set all the way up, all graphics sliders all the way to the left, all the shadows, horizon, etc set as "on". I get a steady 59 FPS (monitor max is 60) in the off-line mode. (Thanks again, TilDeath!)
IIRC, my machine is a 2.6 quad-core I7, with a GeForce 9800 GTX+ video card, and 4 gb RAM.