+1 Single GPU (emphatically!!)
Your original setup was kind of weak - low power cards should really never be put in SLI. Part of the power is wasted in the sharing process. Only get SLI if you can't get a single card in your performance range/budget.
Edit: also if you havent read it you should read this months GPU guide -- http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107.html