Stalker Clear Sky DX10: Slow as molasses

I got Stalker Clear Sky from Steam yesterday and when in DX10 mode the game is slow as molasses like a constant 5-7 FPS, i have everything set to high and 2X AA but if i change it to use the DX9 Lighting and keep all the same settings it runs great 40-50FPS constant.

has anyone else experienced this? all my other games( except crysis) run great also

i find that it looks just as good in the DX9 mode anyways i am just wondering.

Q6600@ Stock
EVGA 9800GX2
Abit IP35 PRO
4 GB RAM
Vista64 Ultimate
180.48 drivers

Same issues on here on a previously owned 8800GTX. Moving to a 4870 1GB resolved that issue. 30-40fps on dx10, max everything except sun rays, etc. were on low.