SLI Help Please!

[dahfizz]

I have been doing research and i do not feel like i fully understand how SLI works. How much does SLI actually increase performance? Can i use the power of both cards to render a game on my main screen even if i have three monitors, or will the GPU's dedicate their power to their respective monitor? If i use three monitors that only have a display port input, do i have to buy three separate GPU's since most GPU's only have 1 displayport output? Ideally i want to use 2 GTX 780 ti cards in SLI and add more if i need to, but i want a three monitor set up and the monitor i want has only a displayport input, so will i have to have at least three cards? I am very confused and if someone could link me to a good article or something I would greatly appreciate it.

 

[Mousemonkey]

You only need a single card to run three monitors but 2 in SLi will improve performance.