People need to understand that DX11 is on its way out.
There. That's the 970 and 980 benched against the RX 480 in nothing but DX12 games. That's every DX12 game (and there are quite a few now, at least five).
In DX12 (which is what matters, DX11 will only come out in games that have been in dev for longer than DX12 has been around) the 480 is 27% faster than a 970 and has more VRAM. It is 9% faster on average over all of the DX12 titles we have than a 980.
Like I said, DX12 will now make its way in and slowly but surely it will replace DX11 completely. Sure, you need to watch out for performance in older games but even then it should perform right around the same as a 970.
Couple of other things to think about.
The 970 is not a new card and production will have stopped quite a while ago. This means it is finite and not a valid comparison going forward. The same goes for the 390 and 390x. Give retailers a couple of months to get rid of stock and they won't be around any more to be bought.
The RX 480 at its proper non gouged and non inflated price is £175 for the 4gb. The 970 is still £200, £25 more. The Radeon has more VRAM and in DX12 its not even a competition.
Seriously, buying a 970 now makes absolutely no sense at all. However, it's probably the only Nvidia card you can compare to the 480 right now. Having said that, the 970 was not a £199 card at launch. It was far more than that.