I'd stick with a 6800GT simply because it's overall a better core, it's got the better drivers and excels overall pretty well in both OpenGL and DirectX based 3D applications.
Why the Toledo/Manchester though? I really think the dual cores are a bit too pricey for their performance at this point and time, get a 3000+ Venice for like 150 bucks, and when more multithreaded applications come out and the prices on the multicores drop, then go out and get one.