Half-Life 2 was once the sweet spot for ATI Radeon cards as they would traditionally win over Nvidia-based graphics cards. The tide turned when Nvidia started winning Half-Life 2 and ATI began winning Doom 3 - this was sweet irony, as most battles between great competitors tend to be.
With the cards at hand, the Radeon X1900XTX has the clear advantage over the GeForce 7900GTX and 7950GX2. This advantage continues with all of the single GPU solutions, but dwindles at high resolutions and when image quality settings are turned up. It is only at 2048x1536 and higher that the dual GPU GeForce 7950GX2 takes the lead.