setting HDRprecision at 0 gives a significtive boost to your performance (obviously).
GTX 280, Q9550, 1680x1050, Fillrate 150%, viewdistance 2000, all settings normal, 20-30 FPS.
Game is playable and nice, still testing...
that's not that great I think, you've got a pretty good rig, and quite "low" perf.
Are you on "all at max" settings?