The demo is on Steam, so grab it if you already have Steam.
And yeh, PhysX is also enabled. Even though I have no compatible hardware I tested it to see what the IQ is. All I saw in the demo with PhysX was just some extra debris. The game looks good even on all low settings.
AMD 5000+ 3.1 GHz, Radeon HD3850
1280x1204, all low no physx
MIN 6.7 fps
MAX 90.9 fps
AVG 40.4 fps
1280x1024 all settings maxed no physx:
MIN 7.6 fps
MAX 62.5 fps
AVG 21.6 fps
The minimum number is completely worthless in the benchmark tool. However the average is right in line with my experience in actual gameplay of the demo. AA kills my performance the most. Without AA I can turn the other settings up. Also ambient occlusion seems to be the second most setting to hit my setup. I turn it off and my framerate increases. I don't even notice a difference, to be honest. I even tried comparing screen shots and don't see a difference. Will test some more in other areas, though.