Finally, the times have come again when you don't have to give a kidney to get a decent card. In our case, the 7800xt is clearly superior to the 4070 obviously. However, you should forget about Ray Tracing and don't expect any improvement in Ray Tracing from AMD in general, as they have stated that they are not interested in it.
16 gigs is the best for high resolutions. It performs well in 2K and can play many games in 4K at 60 FPS. Just keep in mind that if you play in 1080p and many frames (e.g. 240 or 360), unfortunately, this specific card doesn't perform well. For example, with the 6750xt benchmark compared to the 7800xt, I only saw a 7% difference in 1080p! While in 2K, it's over 35%. So I would say it's designed for 2K. It's logical because it doesn't make sense to get such a beast and play in 1080p. Everyone is moving forward, and you're stuck in the past. Let go of 1080p and switch to 2K.
The sexiest implementation of all the 7800 xt cards is the one from Sapphire. Generally, I never had any issues with Sapphire like black screens, flickering, and so on. But I have had issues with other brands.
Don't worry too much about the power supply. Even if you have a 750 gold, you're fine.
However, you should know that you generally need a good PC for your card to perform at its best. It's not just about putting in a card and being done with it. If you have a somewhat old processor, you will see minimal difference, and it will purely be a processor issue.
I've seen temperatures up to 60-65, but I've seen it go up to 85 in hot spots. (Oh, ever since they introduced this hot spot, it has created psychological issues for us.)
Also, if you're into PCVR (I have the Pico 4), that's where you will truly understand what card you've got. At first, the drivers were not good for PCVR. But they have fixed it, and it's working perfectly now.
In conclusion, if you have a 2K 170Hz monitor, a good processor, motherboard, and fast memory, go for it. If you have a 1080p 240Hz monitor, a good processor, motherboard, and fast memory, don't get it. If you have an old processor and an overall outdated system, then you should know that if you get it, you will need a complete upgrade.
That's it.