so here is the way i figure it. Since you were already planning to get build a new computer in the first place adding a couple hundred dollars worth of graphics cards is not going to add the price of the system too much. Also if you were planning on playing games with this computer because the more gpu power you put into this computer the better the games with play, and the more btc you will mine. Also from personal experience i bought a second 5870 for my pc to play games, and mine, and it has paid its self off already. So i would say build you computer and throw a couple of high end gpus into.