Well I expect your 19" gets resolution above or at 1600x1200 right?
If thats the case than in may be worth the few extra bucks.
as you can see the X800 pro fails miserably. You also see that the gt and ultra are about the same at lower res with no fancy aa or af enabled.
So in your case i may well be worth the money for the ultra.
HardOCP's thoughts on BFG 6800 GT OC:
"The BFGTech GeForce 6800GT OC we tested overclocked very well. We were able to not only match 6800Ultra speeds but go beyond them. How is that for getting your money's worth!"
"You will want to keep in mind that BFGTech is an American owned company that operates here in the USA. They give their video card products Lifetime Warranties and have some of the best support we have ever seen out of a retail desktop technology company."
even though its not the ultra it should give you a better look.