I'd just get a single card off this list.
http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107.html

And because of the following statement...
"Our tests demonstrate fairly little difference between a $225 LGA 1155 Core i5-2500K and a $1000 LGA 2011 Core i7-3960X, even when three-way graphics card configurations are involved. It turns out that memory bandwidth and PCIe throughput don't hold back the performance of existing Sandy Bridge-based machines. "
http://www.tomshardware.com/reviews/gaming-cpu-review-overclock,3106-4.html

I'd consider keeping what you have and going up the list in the first link as far as you can go. You have a good machine and bumping up the video would be all I would suggest.
Bob