Anyway, if Vega does manage to beat Nvidia's best offerings, lets face it, it would be nothing short of a miracle
I think it would be expected for Vega to beat Pascal after the 13 months Nvidia's high end has been on the market.
If they don't beat a gtx1080ti by 20 or 30% the Vega is a failure IMHO, especially
with Volta 6 months away from the June Vega release.
WHat do I think? History repeats itself.
I think that big Vega vs the gtx1080ti will be the next 290x vs 780ti.
Before Vega ever actually matches the gtx1080ti performance, Nvidia will release the GV104 Volta (A.K.A the gtx980) that beats the Vega (A.K.A. 290x) soundly.
So ~ January next year the gtx1080ti/Titan x will be old news (almost 2 years old) and Vega (11 months old) will only be a few% slower but the new 35%+ faster Volta gpu's will be the one to have for high end guys.
Vega needs to compete with Volta gtx 2080 performance now, so it needs to be ~20% faster than a gtx1080ti at release and about $650.
If it doesn't, you have to ask yourself," what has AMD been doing for over 2 years"?