I am starting to build my first PCI x16 pc. I am coming from a GeForce 6600GT AGP 8x card and I want to go bigger and better. I bought a board that supports two x16 slots so that some time in the future I can get two cards together. My question is; should I get a single card such as the Nvidia 7900GT or two cards? I am ready to spend up to $350. This computer is going to be for gaming purposes, so what is gonna work better? A single 7900gt or two cards(i.e. two 1800xt, two 6800gt?)