This calculator is better than NewEgg's:
https://outervision.com/power-supply-calculator
It gives 478W for your situation (and that's assuming 4070Ti since they don't have 4070 on their list yet).
850W is huge overkill but keep in mind that for the B650 board you're going to have two 12V EPS (CPU) connectors, so you need a power supply that has two. That usually means only 650W+, or even 750W+ in some product lines. Both are overkill for your case, so you could just go with whatever you can find on the low-wattage end that has the two connectors. Also like someone said, junky power supplies are terribly unreliable. Don't know much about Gigabyte, I only buy Seasonic or Corsair.
I don't think those PSUs are overkill. A 650W is recommended for the GPU he's getting, and he may want to upgrade it in the future and could need more power.
A good PSU can easily outlive your MB/CPU/GPU, so it's better to go with more Watts when in doubt.
I found an EVGA Gold 750W one. All the reviews seem to suggest EVGA works well. I saw some bad reviews for Gigabyte ones and I think my current one is EVGA.
Also, you should be getting a Samsung 980 or 990 SSD, instead of a 970, since you're on a PCIe 4.0 motherboard. Transfer speed is about double and the price is not much different.
Thanks for the recommendation. I found a 980 SS for only £30 more. The 990 seems a tad overpriced and doesn't seem to provide much more of an efficiency gain to me. Unless I'm missing something.
It's hard to make recommendations if you're not planning on upgrading until the end of the the year because a lot can change (and also stay the same)
I've had the upgrade bug for a few months now and if I were to buy today or soon it would probably be some thing like this:
CPU - AMD 7600
MB - Many choices, I would stick with Asus, Gigabyte, or MSI
GPU - Radeon 7600xt or better for AMD, Nvidia 4060 (if it's available by the year end) or 3060 12GB
DDR5 - 32GB 5600 or 6000 (Gskill, Teamgroup)
SSD - WD 770 M2 or Crucial P3+ M2, 2GB
PSU - depends on the case and overall setup. Probably 750w minimum gold certified. Always go fully modular. Corsair, Seasonic have always been reliable for me. You can search for PSU tier lists.
Yes, I know. I'm a bit odd that way. Because I find my PC still works well enough for now, I don't see the point in upgrading today. But I also don't like making impulse buys, so that adds to researching things now. Of all the new games coming out this year, the most demanding one for me will likely be BG3 and that was running fine on my current set-up when I tried it out in EA.
The only games giving my machine trouble tend to be heavily modded Unity games (BattleTech - looking at you), which I think is due to the engine more than my set-up.
From what I've read - you may as well go for the 7600x as it's only $10 more or something and it's better.
I've never had an AMD GPU, so I feel a bit odd about changing to them. Most benchmarks I've seen show them underperforming compared to NVidia's lineup at same prices. The only exceptions seem to be games which a crapton of VRAM, which there aren't many as far as I know.
For RAM, I don't know how much the brands make a difference, but the one I found seems to have pretty good reviews.
PSU, as above, I'm looking at this:
Also, I found a case I like more, but it's more expensive:
https://www.amazon.co.uk/gp/product/B07N1MBZ1W/ref=ox_sc_act_title_3?smid=AY4WCH984Q0C2&psc=1
Also, thank you everyone for the contributions. Much appreciated.