4 980 Tis is actually one of the stupidest things you can do (it has nothing to do with money). It has to do with how SLI works:
SLI for some reason will NOT use all the power out of 4 cards, this is why 2 way SLI is pretty much the max you'd want to do for an optimal expereince. 3 way and ESPECIALLY 4 way SLI brings in a lot of latency issues, and the 3rd and 4th cards aren't even at 50% load at any given time.