Look at some of my screenshots from earlier in the thread to see how well it scales (hrmm). But I am playing it on max, at 1920x1080 and my framerate is usually in the 60-80 fps range (using a Radeon 5870). I've seen it go as low as 25-something fps (during an orc attack on a city) and it's constantly above 200 fps inside dungeons, so it varies wildly. It really depends on your setup.
Alrighty then, I'll pick it up on Steam when the crazy March rush (??) passes over...