There are PROS and CONS to both methods.
The SLI will give higher performance, but is more prone to stutter, and costs a little more.
My advice is to get THIS card:
EVGA GTX780 967Hz model (with ACX cooler)
As for TWO monitors, it doesn't matter if one's a non-gaming monitor and I wouldn't recommend gaming with only two of them as the gap is in the middle.
If you had THREE it would be a different story, but then I'd be recommending at least 3GB per GPU anyway thus a 2x780 or 2x(GTX770 4GB).