No, you're absolutely bamboozled. I run three monitors, one 120Hz for gaming, and two 60Hz for monitoring my PC and daily updates.
There's no difference when gaming between having those monitors connected, and not using them.
You also don't even come CLOSE to needing two 780s - give me a break! One is more than enough to max games on your resolution... and buying two just to run a monitor off the second is just silly.