I have a 6800Gt sitting on AS5 and zalman fan.
I would go for a x800GTO2 or GTO. I know the GTO2 can be unlocked
Newegg has the x800gto2 for 165 shipped
If you have had a 6800 you wont get ahuge performance boost unless you go for an X850XT or so, they are avaiable in AGP not sure on the price though. otherwise maybe you should look into a 6800GT or 7800GS type of card, or even a new cpu/mobo/vcard might be cheaper for you