The chaps over at PCGH have published a batch of DX10 benchmarks for S.T.A.L.K.E.R.: Clear Sky using some 11 different video cards. Here's a taster:

Stalker: Clear Sky knows only two ways of running: very slow or absolutely playable. Depending on the scene or level the framerate is below 20 fps or climbs to more than 40 fps - but we experienced the former to happen more often. Anisotropic filtering is recommendable since it doesn't cost a lot of performance. But you should abstain from any kind of anti-aliasing. MSAA already lowers the fps without improving the optics very much. Better graphics can be achieved via transparency FSAA or SSAA, but both modes are unplayable in Stalker: Clear Sky. In higher resolutions at least, the graphics cards with a lot of video memory can beat their less equipped competitors. The Geforce 8800 GTX for example is 14 percent faster than the 9800 GTX+ at 1,680 x 1,050. AMD's HD 4800s are doing quite well - we cannot confirm the rumors from Russian forums that the Radeon cards would deliver insufficient performance only. The Geforce GTX 260 seems to suffer from driver related problems. Multi GPU systems are scaling extremely well (up to 100 percent) with the X-Ray Engine - not very surprising since the engine is not new. A special multi GPU article with videos will be released by next week.

If you want to play Stalker: Clear Sky with all details in DX 10 a t a resolution of 1,680 x 1,050, you will have to use a multi GPU solution. If you don't need high framerates you can do with Geforce GTX 280 or a Radeon HD 4870. At 1,280 x 1,024 a Geforce 8800 GTX, 9800 GTX+ or a HD 4850 do quite well, but you will have to go down to 1,024 x 768 to make them display the game really smooth. Stalker: Clear Sky requires a lot of RAM and video memory. Currently we are testing what processor is best, but at the moment more than one core seems to be useless.