2080 Ti is 40% stronger than the 5700 XT. And how much stronger is the top Ampere likely to be over the 2080 Ti?
That's part of the problem. I don't honestly believe those rumors took boost clocks from the best OC cards into consideration. Just standard OEM card.
(At a guess)
So, using the best OC 2080ti...
3070 would be about 20% improvement
<3070 TI variant> would be about 25%
3080 would be about 30% improvement
3080 TI would be about 35% improvement until 3080ti OC cards come out then about 45%
3090...unknown at this time.
So, if 40% is the deficit Big Navi would need to be more then 5 FPS better on average...
Big Navi about 60% better then a 5700xt to handily beat a 2080ti OC, at it's highest boost.
Big Navi would need to be about 85% better then a 5700Xt to beat a 3070/3070TI.
From then on we are look at well over 100% to beat a 3080 and it's variants.