The only problem is cost. I figured if I do end up building a new system, it would cost me over 2 grand easily. I plan on beating Crossfire with dual 7800GTX and I may be crazy at doing this knowing it will not even make a dent in most games out there. Mainly the motherboard, graphics card, and memory is where cost will get to me. I don't plan on a sound card at all. Most SLi supported motherboard have fairly nice 5.1 surround sound and if I choose the Abit Fatal1ty board, they use a 1x PCIe slot with an included sound card. I think having dual 7800's will limit my space for a sound card anyways because I plan on adding an exhaust blower right below the video card to relieve some of that hot air out.
Maybe I shouldn't be too greedy and stick to just a single 7800GTX eVGA card. That card is probably the highest clocked 7800GTX I've seen so far, stock.