Well the heading says it all. I currently have the gtx 680 4gb edition and ill be running 2560x1440 on my new monitor at 120hz and idk if i should go titan, 690 or sli?
If you have $1000 dollars to burn go ahead. If not save the money or maybe even invest it? Gold and Silver prices are at 4 year lows or better.
Not very many games can use SLI or crossfire very efficiently and those that do stutter from what I have heard. Also 2 cards would make your computer run hotter unless you are putting everything under water cooling.
For a single card solution one Titan is enough for anything.