You say the screen is limited to 30hz?? If that is the case, slam vsync on and you have a steady 30 fps without tearing, as you said it doesn't drop below 40.
But yeah, I'm sure you'd be aiming for 60hz minimum if you were to acquire such a setup. I have been playing on an i7 4770k with a 3gb 780ti, DCS installed on a pretty savage ssd and with 16gb of fast memory and the fps does drop at points. But it usually picks up again once the viewed scene complexity drops. I can only imagine the SLI is not playing nicely.
Sli and x fire are, in my opinion, lame.
Why would you pay twice to get way less than double performance when you could spend almost the same money and get a better single card that is much closer to the golden 2xpower goal.