A few days ago PC Perspective got their hands on a beta version of this game and they ran some tests to see how much the PhysX chips improves performance.
For our testing we ran the same levels both with and without the AGEIA PhysX card installed. Important!! You will not be able to do this on the copies that are available for download today but press copies were allowed to manually enable and disable PhysX card support in the menu regardless of whether a card was installed.They found that the PhysX dramatically improves the performance. The min FPS jumps from 4FPS to 13FPS, the max FPS from 12FPS to 55FPS and the average FPS from 8.3FPS to 32.1FPS in the Reactor level.
You can download the game for free at Gamershell (859.6MB).