You say 30-35% as if its never lower. Some reviews have it averaging lower than that and in some games its only 15-20% better. The 980 ti also has more overclocking headroom so at the end of the day it would be a pathetically small upgrade when looking at oced 980 ti to oced 1080. I still dont get all this praise as in my opinion this card is a joke for a next gen product at 700 bucks.
The price is a bit high, but for a 980 replacement is does bring pretty good performance. You have to remember that this isn't the 980ti or Titan X successor.