Anyone have experience playing this on lower-end machines?

Just downloaded the game (Thanks for everyone for all the help in my topic a few days ago), and I am curious about the performance on lower end machines. I watched a graphics option video a while back and lower quality didn't really seem that bad, though I think the video quality wasn't that great, but still good enough to tell the differences.

My machine isn't terrible, but it is by no means great by any standard (phenomII x4 black, HD6750, 4gigs of ram, win 7 64bit). I'll probably have to settle with running this at low/medium. Just curious how the game runs with similar hardware. Is the game decently optimized yet?