The performance is definitely worth it to go with the 1080 if you have above 1440p (1440 21:9) or VR/4K displays. 20% is 20%....the 980ti was already a little underpowered in single form and the 1080 helps bridge that.
Agree though, for many cases that the 1070 will get the job done fine. OCing the 1080 also seems to help more with higher resolutions vs 1070.
It's surprising how close they ended up being. I think a REALLY good 1070 model will be the price/performance sweet spot for anyone above 1080p until P10.
4K
DAI = 35 FPS
The Division = 41 FPS
Far Cry Primal = 42 FPS
Assassin's Creed Syndicate = 42 FPS
The Witcher 3 = 49 FPS (no HairWorks)
Metro Last Light = 46 FPS
Rise of the Tomb Raider = 46 FPS
Shadow of Mordor = 61 FPS
Fallout 4 = 37 FPS
Hitman = 42 FPS
GTA V = 40 FPS
http://m.sweclockers.com/test/22153-nvidia-geforce-gtx-1070/5
Even with 0 GameWorks features and 0xAA, 1080 OC cannot hit 60 FPS in modern AAA games at 4K.
https://youtu.be/XdN9DxR-JVQ
25% extra over 980Ti OC/1070 OC is a drop in the bucket for 4K gaming when what's needed is 50-80% more performance. That's why for 4K gaming 1070 SLI is still better. A single 1080 is a pointless videocard. Overkill for 1080p 60Hz, pointless for 1440p 60Hz, not fast enough for 1440p 144-165Hz or 4K 60 FPS average. The exact definition of a No Mans Land videocard -- exactly what I said when the Original Titan came out (too fast for low end resolutions, not fast enough for next gen games or 4K). Since 1070 also costs much less, it'll be far easier to sell as there will be a bigger market for it. Once 2017 cards hit the scene, 1080's resale value will drop big. Just like today there is hardly anything better than a $200 970, making it an easy sell, but try selling a used 980/980Ti for close to their MSRP around launch?
1080 is a repeat of 980--only purpose are paper benchmarks to say it's the fastest. In practical terms, it's not going to provide a much better gaming experience where it counts. It's exactly why many 980Ti users were disappointed by it. It's another waste of $ videocard against 1070/980Ti and 1070 SLI.