The 7970 aged much better than the 680 and is still useful in modern games today, while the 680 can be around 25-30% slower. Lack of VRAM probably doesn't help. Although I can't see 16GB Vs 24GB being an issue even at 4K. I imagine 12GB will be what most people will need for gaming for the next 5 years. The 30 series from Nvidia shafted gamers with its low VRAM amount, I say this as an owner of the 3060ti.
I can confirm that, two of my brothers, one bought the 680 and the other bought the 7970, the 7970 was £30 cheaper than the 680, it had 1GB more memory then the 680 and aged a lot better over the long run.
Early on, performance of the 7970 was around 7% slower on average compared to the 680 but overtime, it gained a lot of performance and ended up being around 25% faster than the 680, depending on game, it was a cheaper card, had more memory and better performance, it was a better card at the time with the only real downside is that it used a bit more power but the gap was pretty small compared to gpu's today.
As for the 7900XTX, it's remarkable the performance is where it is with the mess the drivers are in, it wouldn't surprise me if there are some big performance gains on these cards over the long run and a little hint could be with how the performance is all over the place per game.
If I was buying this card, I would buy going on the performance it delivers now, if you're happy with that for the price, you're good, performance overtime is likely going to get better, more so than the 4080 will and if ray tracing isn't that big of a deal, it's a decent card but even with ray tracing, we're still talking 3090ti level of performance, so the 7900XTX is still good at ray tracing, that might get better with more mature drivers but Nvidia will likely lead on that this gen.
Personally, I wouldn't buy any of these AMD or Nvidia cards, both are overpriced and in the case of AMD's cards, it's better to wait for the drivers to mature, performance, stability is likely to be better later this year and the price might drop because none of these cards from both companies are selling in the current market.