Pulled the trigger on a 7900X today since my ex-company is finally sending someone to take back their 5950X based workstation (about 4 months after they said they would), and I am not going back to the old 4770K!
I was tempted to go with the 7950X as slightly faster compile times would be nice, but figured the 7900X is fast enough, and I'll probably upgrade to a 8950X or 9950X (or X3D) in the future anyway and stay with that for a good long time, so I view the Zen 4 CPU as transitory (however, even then, the parts below the 7900X just don't make much sense to me.)
For the motherboard, I ended up selecting the X670E Pro RS. Still not happy about the price, but I plan on keeping it through at least one more AM5 processor and I expect to eventually make use of the PCI-e 5. Every other X670 board either looks disproportionately crappy without saving much money, or disproportionately expensive without providing much additional benefit. The lack of much in the way of PCI-e expansion slots is the big drawback that might become an issue at some point, but that seems like the only real weakness... and I think the integrated GPU support bracket is ingenious.
Edit: A day later, the X670E Steel Legend went on sale for the same price, so I ordered it and will send back the Pro RS.
I think I'll buy memory closer to the time the rest of the other parts are due to arrive, looking for deals over the next few days and using price match/beat at my local store (Memory Express). Wish I could do 128 GB, but will have to settle for 64 GB (32 GB is right out of the question). Currently mulling over whether I should go 5600-CL36, or save a few bucks with 5200-CL40, considering I expect whatever processor I end up upgrading to in the future will have some sort of magical cache and memory speed / latency simply won't matter much at all.
I think if I had been able to wait a couple more months I might have been able to save a couple hundred dollars more, but if I had to build a new system even a couple months ago, I probably would have went with a 13700K with DDR 4 like I built for my dad. With today's prices, Zen 4 finally makes sense--but only when you factor in the upgrade path. If I knew someone would just hold onto the same PC until the post AM5 period, a DDR 4 13700K is still around 2/3rds the price while being pretty comparable for production workloads (the difference in gaming, imo, just doesn't matter).
GPU wise, going to slum it a while going down from the 3080 Ti in the workstation to my old GTX 980. It's way more money than I want to spend, and I definitely don't want to pay over MSRP, but I may pick up a 4090 just for its AI abilites. I'm hoping the release of the 4090 Ti will cause some downward pressure there.