There's far too much misinformation right now. Seems like a lot of people skipped math class...
What are you upgrading from, and why on earth would you be willing to pay 599 dollars for a 1080, when a 980 Ti is better, and cost less?
I think people forgot that GPU's are improved by roughly 10% each year, forget about NVIDIA's claims, completely. They would be making the biggest business decision if they did that, of course they are using skewed graphics to fool the unaware...
The 980 Ti is 50% ahead of the 980 in DX11, now NVIDIA are using DX12 for whatever reason in their "claims", and they're claiming a ~70% increase over the 980, which is realistic considering the MSRP, and the current price of the 980. But they're not honest about it, they specifically say performance and power consumption, they don't tell us the FPS or anything. Welcome to marketing.
All the best!