I've got a 6800 Ultra in my pc currently. Is the 7800 gt so much better that I should upgrade or is the difference minimal? I havent seen much comparing the two yet.
If I were you, seeing you have the SLI board, I would just add another 6800U. That 6800U will last for a while, maybe a year or two. So once prices fall, add another one. Don't do it right now; I think you won't see much of a difference.