S.T.A.L.K.E.R. - Clear Sky
S.T.A.L.K.E.R.: Clear Sky, is the stand-alone prequel for S.T.A.L.K.E.R.: Shadow of Chernobyl, a first-person shooter computer game by Ukrainian developer GSC Game World. The game consists of a roughly 50/50 mix of new areas and old, remodeled areas from the previous game. The X-ray graphics engine has been updated to version 1.5 and includes DirectX 10 support (later patch 1.5.06 included DirectX 10.1). Additionally, the AI received an overhaul to accommodate the new faction wars feature.
HD 4850: Performance is down and all over the place here. And no those minimum results aren't backwards.
HD 4870 X2: Minimum's seemed to have dropped off slightly.
HD 4890: Here we see no real change.