770 sli or r9 270x 4way crossfire???

Traciatim

Distinguished
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.