Just to point out, AGP 6800s are the only ones that can be unlocked. PCI-Es cant, because Nvidia saw how great the yields were for the 6800GT AGP and just made seperate chips for the 6800s for PCI-E.
Also, The Pixel 3 thing actually hurts performance of the cards, doesn't help them. The reason is that it puts much less stress on the graphics card to do 1.1 than to do 3.0. Think of it as having 4x AA compared to None. 4x AA will look awesome, but you will take a perfomrance hit, while no AA will not look as good, but you will be flying compared to the 4xAA guy.
So in conclusion, the 800XL is a great buy, priced at 250. Although it will not support Shader Model 3.0, and many developers are going to cut support for shader model 2.0 in the future, it will still run many games in the future. Remember, just two years ago (I think), the 9700 Pro was the top dog. It was able to run AA on the latest games no problem. Now, It would be very hard to run AA on games like half-life 2 without hitting a performance pit. This is like the 6800GT right now. It is a very good card right now, but in 2 years, when games improve even more, it will be very hard to justify running AA, and having SM3.0 may actually be a hinderance to decent frames.
I do not know what the next generation games will require in performance, so my analogy might be flawed, but If you were to decide between a 6600GT and an X800XL, I would go with the XL.
6600GT PCI-E for sale/Trade. Check the FS/FT forums on tech-forums for details.