The 9800 GTX is NOT a high-end card. It is on the high-end of the mid-range cards.
Look at the price vs the GTS 512, and look at the performance. Just about the same.
The 9800 GX2 is a much better upgrade.
If the 9800GTX had a higher memory bus/memory it would be something worth commenting on. But it doesn't so I wont.