You will win FPS benchmarks with GTX970 sli.
But, at only 1080P, I think a single GTX980 will be a better experience.
dual cards may have issues such as screen tearing or stuttering because of minor differences in performance of separate cards. And... some games do not do well with dual cards.
Look for a factory overclocked GTX980. The small premium gets you a better bin and a warranted overclock for not much more.