The GTX580 is a dual core GPU right? So I'm assuming by 4 way SLI you mean you have two cards with a total of 4 gpus?
Yeah, I'm hoping to build something like that in around a year, possibly two 590 cards. Every penny of my wages is going into the bank to get saved
I think the Xeons might be overkill, mind. A 1366 I7 would be more appropriate