We used the built-in benchmark included with World In Conflict (the demo version), and tested in Vista, in DX10. For the second set of charts, we used an AA seting of x8, and AF setting of x16. The Asus EAX X1950 Pro is incapable of rendering in DX10, so we ran that benchmark in Vista/DX9, and put the results in the chart for comparison. (And by the way, if you read my World In Conflict Performance Review, you'd probably agree that the DX10 version does not look much different than the DX9 one.)
The RX2600XT Diamond Plus does not perform too well here -- but this is likely more a reflection of the current state of ATI drivers than anything else. For evidence of this being the case, you need not look further than seeing the HD 2900 XT score below the 8600 GT. Just recently, Catalyst 7.10 was released. The release notes state that World In Conflict performance has been increased. Hopefully the 7.10 Vista drivers will deliver the goods for all the ATI / World In Conflict / Vista gamers out there, because the game's performance with Catalyst 7.9 leaves much to be desired.