Becuase of something to do with the fact that the 9800GT isn't optimised for 1gb memory. At high resolutions yes the 1gb will come in handy but at standard reses the 512mb out performs it.
Thought it might be something like that. Remember when the 8800gts with 640mb was seen as perfect for high resolutions and the 320mb was for standard res's?
Ah but I now have 2 in sli so I am only just behind you. I went about 6 months thinking I had the 320mb then randomly checked with everest whilst OCing and was surprised they had made the mistake and upgraded me to the 640meg
Thought it might be something like that. Remember when the 8800gts with 640mb was seen as perfect for high resolutions and the 320mb was for standard res's?