Thanks for the feedback so far.
CPU
Wilco on stepping up to 5600. It's only $35 more at newegg right now at $135 on sale. 5700X caught my eye at $199, but I presume it's not worth the additional cost from a value perspective.
Memory
Leaning towards Gskill Ripjaws 32GB 3600 cas18 at ~$88. I may as well spend the only ~$40 extra now then wish I did some years later. I'll consider any sales pitch to go 1/3rd more $ for cas16 if it's worth doing so from a bang-for-buck perspective.
Motherboard
@AusWolf ASUS TUF B550-PRO, I presume? Hum, only $5 more at ~$145. I've always thought of MSI motherboards as a bit rough around the edges, but with so many positive reviews and this being the most matured point of AM4, I kind of wanted to go non-Asus this time around. Less drama for $5 more is a compelling argument though, if that's indeed the case.
@eidairaman1 Hum, AsRock B550 Steel Legend even on sale is another step up on cost. I'll still check it out. In the past I've always been too wary of AsRock (and Biostar) to ever go that route, but AsRock has gotten better mindshare for me in recent times.
PSU
My quite venerable, now totally dead build kept getting additionally iffy over the last few years, but it was still quite usable, so I eked along. For the last few months of it's life, I put in a new RM650x to see if that would fix anything, with the rational that I could use it for a new build later if I had to go that route. No change. For the last month or so of the computer's life, when I would press the power button, it would power on with GPU fans at full speed (others fans at constant undervolt), but nothing beyond that e.g. no drive detection, no post. If I left it for a bit in that state, then held the power button to cut it off and then tried turning it on again, it would then turn on successfully and could be used. Once it became dead as a doornail, I went though the effort of looking over the motherboard (SPCR-spec quite build, so a bit of a pain to take apart). Even though I didn't see any bad capacitors, I'm presuming something on the motherboard front finally died.
TLDR: I plan to use the RM650x from my old build -- unless you guys may feel there's considered concern my old hardware may have damaged it. Let me know what you think. The last thing I want is to damage new hardware. Side note: Covid killed the last shop in town I'm aware of that might have been able to do a PSU test for me.
GPU
I'll continue to use a Kepler from my old build for now.
Storage
MX500 from old build is fine for now. I think I have a half-length 512GB NVMe too. For sure some additional 2.5 SSDs. And I have a multiplicity of 3TB work-retired rust and a NAS for slow storage. All set on this front for my current purposes.
Case
P182 from old build. Fine for now at least.
Heatsink and Fans
Thermalright Ultra 120 and Sycthe S-Flex and Slipstream fans from old build. Fine for now at the very least.
OS
I've been running Linux exclusively for my personal stuff for quite some time now. Steam on Linux scratched most of the gaming itch. I may bother to throw Win10 on a separate partition, probably only once desire to play a truly WinOS-only game overcomes my apathy. (I did WinOS desktop admin work long ago, and Microsoft basically annoyed me into going down the Linux path. For some time in my professional life, WinOS desktop and sys admin work is gloriously someone else's annoyance.)
