don't waste your time running more than 1 graphics card. ATI and Nvidia both are plagued by stuttering and driver issues when running 2 or more cards. its a marketing gimmick (i bought into it a couple times hoping it would get better).
you'd be much happier getting a single beefy card that can perform at the speed of the 2 cards. you'll have smoother frame rates, and a better experience.
some people will say "SLI works for me!"
it does.... SOMETIMES. when it does, it works nicely. when it doesnt, you've wasted your money lol.