SLI and Crossfire generally don't scale well over 2 cards. Sometimes it works, but many times it's a pain to get going properly and can, in very few cases, even hurt performance. You are probably better off getting the best single card you can or possibly doing a combo of two cards that get better performance than the one for a better or similar price. Beyond that it's pretty special purpose use, mostly for doing multiple or crazy high resolution screens.
between the two options, GTX 770 x2
4-way SLI or CF is pointless, even with cards like the GTX 780Ti. Of course the GTX 770 will be more powerful, look at the price tag.