My advice is just get one card.
Even though you have a 1440p monitor, many games like Skyrim will look almost exactly the same at 1080p (on the same monitor). I mostly game at 2560x1440 only on games like Diablo 3, Starcraft 2 etc because the small text/HUD does make things noticeably better.
Of the few games that might drop below 60FPS you can easily tweak the quality settings to look great and still get a solid 60FPS experience (I run at 60FPS VSYNC ON).
Personally, I wouldn't spend $720 more for the very small visual difference you'd get. Your system would also be a bit NOISIER as well.
Be VERY CAREFUL reading reviews to find one that has no coil whine issues like the latest Asus version.
THIS EVGA model might be the best one but I don't have time to look further:
http://pcpartpicker.com/part/evga-video-card-03gp42884kr