Realistically though, 60% more performance at 5-10% more power consumption would suggest more like 50% gain in efficiency.
Obviously there's no hard data on performance, but I'm mostly taking nVidia's own very basic (and no doubt heavily "massaged") slide here:
The other thing to bear in mind is that the 980Ti has a lot of room for overclocking, and I reckon a heavily overclocked one could probably match a stock 1080 given the estimated difference of 20%. Much of the 1080's value then will be in how much it overclocks in turn.
EDIT: Another of their own slides here might be more instructive. Eyeballing that shows an approximate rating of 2.6 for the 980, 3.6 for the 980Ti and 4.4 for the 1080. Normalising the figures to 100%, we get 1.38 for the 980Ti and 1.69 for the 1080. Normalising the 1080 vs the 980Ti we get 1.22 which is pretty close to my earlier estimate.
980Ti is down to $550USD now, and the 1080 will roll out later for $600. It barely moves the price/performance stakes at all. The "Founder's Edition" (early access reference design) card for $700 is particularly laughable in this context, it's for suckers only.
More speculatively, if we take the same 3.6 value to be the 1070's performance, that's 1.71 relative to the 970 at 2.1. A slightly bigger increase in relative performance to the card it's replacing, but at half the price increase (or two-thirds in relative terms). I reckon that's fair enough, it's around what I'd have guessed prior to the reveal.
Edited by Humanoid, 10 May 2016 - 12:48 AM.