Isnt 1860mhz the boost speed? Did you ever think that perhaps NV class boost and OC over standard speed an OC?
See they classing it like that is already false marketing hype because it's fake.
Go check out OC reviews for the 1080, they don't get 25% extra performance at 2.1ghz. Because that's not how OC works for NV GPUs. You don't look at base clocks and compare that to your final OC clocks.
As @iiiankiii said, the performance at stock, is from the higher than paper spec boost clocks.
980 and 980Ti reference boost to 1.2 to 1.25ghz, well above paper spec. When they OC to 1.5ghz, they gain around 20-25% more performance. That's good OC.
The worse thing is the performance in benchmarks aren't even reality because gamers have their GPU inside a case, not an open bench optimal condition where boost clocks are higher. After 10 minutes gaming inside a case, as you may know by now, the reference 1080 throttles hard. Some reviewers find it running at base clocks. That's a loss of over 250mhz of performance compared to the first few minutes of it boosting at 1.89ghz.
A gamer sees benchmarks, woah, nice numbers, comes home, games in his case and now it's under performing by 10-15% unless he cranks up the fan so now it's noisy.
So please, next time don't say stuff like NV doesn't falsely hype it's products, it happens to every single reference card out there.