i've heard the x1900xtx actually performs a little better than the 7900GTX, but if i remember right it is a bit more expensive. IMO it's best to look at the very top of the line and then go a little down from that when you get PC parts. That's the sweet spot for the price/performance ratio. If I were you, I'd get a 7900GT or two for SLI. It may not perform exactly as fast as the gtx, but the price is significantly lower and you'd probably replace your GTX or 1900xtx in the future anyway.