Bang for buck would be the best expression. For around $360-80 you can overclock a 970 and hash nearly 6k, and only pull around 160-70w. Super efficient! I would go so far as to say that a gtx970 is as, if not more, efficient than a 750ti. But that's speculation, as I don't own a 750ti.
Update 10/28: got my GTX970 FTW yesterday. been mining for the past 8 hours, underclocked 1177mhz, 59% power target, pulling no more than 170w, hashing 5.5mh