Don't know where you heard that but a gtx 1080 at 2025mhz running same map, same res and same settings is faster than the shown VEGA.
Obviously when VEGA is released with better drivers, overclocked etc. I expect it to be faster than the 1080 personally. Although depends entirely on its DX11 performance too and we haven't seen much of that yet.
From Doom112 himself. I linked that same chap and he clearly states his GTX 1080 is running at 2.25Ghz, along with the 5960X at 4.5Ghz
You're telling me I cannot buy a GTX 1080 running at 2250Mhz base clock right now?! 

