780 is a very very nice card, if you can afford it and it won't bottleneck, get it and run triple monitors xD
770 is also a very powerful card, and I'd only suggest you to SLi/CF if you were doing an upgrade or you were going to run them through a GPU water cooling block and OC the crap out of them, don't care what SLi/CF it is, I usually don't recommend it as most games run best on a single card.