Originally Posted by brettjv
Either the Asus ARES or the Sapphire 5970 Toxic 4GB.
Of the actual realistic (i.e. semi-affordable) choices, the two best are the 5970, and the GTX480.
PCI-Ex 1.1 16x is not that much of a bottleneck for any card out there, honestly.
But the processor might be. What are you going to get for a CPU?