Just get a Titan Z. But honestly Civ 5 and Payday aren't the most graphically intensive games. I run those at max with my 670 and have no problems. I do get noticeable frame drops on Total War Rome II but I think that partly has to do with the poor optimization of the game. I couldn't imagine running it over 3 monitors however.
Currently I am thinking of picking up a new processor/motherboard and upgrading over time. I'd love to just buy 980 but I think my 2.8 i7 is holding me back at this point.
