So, the motherboard I didn't overpay for. It's an ASUS ROG Maximus Extreme Z690, it's still listed at the same price ($1089 before tax), but the GPU I definitely did. I looked for many different versions of the card, and in the end the best deal I could find was the Founder's Edition. I had been looking for the ROG version, but the best price I could find was about $3,500. In the end the Founder's edition already massively exceeded the capabilities I needed anyway, so I saved the $800 and went for that. The DDR5 RAM is still running at about $85o-900 for the 64gb, especially for the Corsair Dominator Platinum series. I paid a huge premium on the GPU, double the price in fact, but I had a short window to take advantage of it, so I wasn't too bothered. If it had been my own money, I would have waited. The 12900KF, which I have, I believe I paid about $900 for, but can be got now for more like $500. And yes, this was all during the peak of the chip shortage.
I also looked up the PSU, which is a Be Quiet! Dark Power Pro 12 Titanium 1500W. It is completely silent, very efficient, and rated about the best PSU you can get. And it better be, it was $600 with tax.
I am not currently overclocking the GPU, only done some minor CPU overclocking. I haven't really unlocked the full potential of this system yet, but I have been prioritizing stability and durability more than anything, because the base clocks and cores on everything are already so powerful, that I don't feel the need really for any overclock.
I had been using ASUS's AI overclocking suite, which had been running the 12900K at 5.5ghz on the 8 performance cores. The remaining 8 productivity cores running slower. But I was having significant system instability issues. The AI just wasn't smart enough to not overdo the voltage and I was BSODing under consistent stress. Since then I have deactivated the AI OC suite, and been running at the base turbo of 5.2ghz, and have started experimenting with manual settings to find the sweet spot for me. I can easily do 5.3 without any worries. The ROG Ryujin 360 II keeps the core incredibly cool, and the cooler master case is very spacious and has amazing venting from a completely sealed environment. I am now going to push it to 5.4ghz and see if I keep it there.