Cheapest 6800XT I can find in Germany is 600€ and cheapest 6950XT is 670€. The 6800XT has roughly the same performance in gaming as the 4070 but worse performance in everything else. The 4070 would also save me 70€ a year in energy cost. So the decision isn't really as easy as just comparing gaming performance and sale price and calling it a day.
And the Nvidia card will be 70€ cheaper after 1 year when you factor in energy consumption.
That is presuming:
1. Your power supply can handle a 300-400W GPU (at sub-200W, the 4070 will easily run on more modest PSUs, very important for SFFs);
2. Provided your power supply has the capacity, ensure that it can handle the transients and spikes that a high-wattage GPU will produce (which is another problem in itself);
3. Your PC's cooling can manage the 6800 XT's high wattage (the 4070 will exhaust less hot air inside the case due to its lower power consumption);
4. Energy costs remain constant (they are ballooning up in Europe, and in a general trend upwards worldwide)
5. You absolutely do not care about having features such as DLSS and the NVIDIA ecosystem and;
6. You absolutely do not care about resale value in the future;
7. You buried your head in the sand, set your foot down and absolutely refuse to accept that DX12 Ultimate and raytraced games are here to stay - with ideological fervor
Then yeah buying leftover stock of 6800 XT makes sense
If you still turn on RT at that level, you are only letting go of about 15% performance with AMD, which I would not consider earth shattering in any way.
What the 4070 has going for it is fake frames and encoding. But a lot of people will overlook those in favor of 10% more raster, especially at the mid range where it counts more.
In any case, AMD will eventually launch something as well. My point is that they don't need to rush because the 4070 is not very impressive.
15% frame rate loss on average with RT on is something not even Ampere will manage. Usual frame rate hits on Navi 21 are in the 40-45% range, unless you use the lightest raytracing options possible. This becomes significantly more severe if it's a high resolution where the GPU is bandwidth starved and/or cache hit rate is reduced.
Regarding RDNA 3: it is exceptionally unusual that AMD, the supposedly consumer friendly company, hasn't serviced the highest volume markets in the midrange, and i'll call it: that reason isn't that the midrange is supplied by previous generation overstock. It's because if the 7900 series are anything to go by... they have a stinker in their hands.