Just for a second, forget that extra 1GB VRAM and the low power usage of 900 series. And just try to decide between these two in raw performance.
Which one would you choose?
I managed to get my hands on a very cheap(but new) 780Ti Kingpin Classified(1450TL and 970FTW is 1200TL(roughly 100usd difference)), and I'm insanely tempted to buy it. But when you decide, I want you to take into account that I will OC the card as much as I can on Air(and maybe even liquid if I'll buy 970).
780ti Kingpin hands down overclock the Kingpin card will make the 970 look like a tiny little baby card.