Besides the obvious (cooling) I'm aware that there's a highly complex relationship between memory parameters (speed, latencies, even module capacity, and maybe # of modules, etc), that different motherboard chipsets and bus arrangements affect speed, that memory modules themselves can suffer from speed degradation based on their chip layout and controller(s) on them, that I/O arrangements and hardware (e.g. multi M.2 PICe4 RAID) affect SSD [not really part of my question, but, I don't want to sacrifice I/O speed in my max-processor-performance quest here] ... and there's no doubt even MORE that are important that I don't know about [gpu probably isn't relevant or affecting cpu performance here, but I'm not totally sure].
I'm also aware that over-clocking can be possible (affecting all the above even more), and in particular, that "faster memory causes slower performance" because the optimal we want is to match the Infinity Fabric's (possibly overclocked) speed exactly to the ram we're using (if there's no match, everything has to wait)...
So - What, as of right now (July 18, 2021) is the peak in performance for this chip? For arguments sake, lets say I want to come top in this chart (the user submitted benchmarks): 53,480 CPUMARK: https://www.cpubenchmark.net/cpu.php?cpu=AMD+Ryzen+9+5950X&id=3862 (although technically, single-core performance is my most important metric, without sacrificing too much the overall cpumark).
More info about my motivation and research into this is here, FYI: https://forums.whirlpool.net.au/archive/3kvzvx09
There is trillion of reviews where answer for your question is provided. I will take 7-zip example because there are the biggest differences.
As you can see, the highest performance is 4 modules and with two modules there is significant performance decrease. This is because reviewer used 2 pieces of single rank modules. Two pieces of dual rank modules has similar performance to 4 pieces of single rank modules.
To answer your question directly, buy 4 pieces of single rank or two pieces of dual rank modules 3600MHz CL14 because FCLK more than 1800MHz is difficult to achieve.
Looks like these are the cutting-edge for RAM: https://www.gskill.com/search?keywords=CL14-14-14-34
My research says X570 is the only chipset to get (others do not use PCIe4 speeds); this looks like a good mobo: https://www.msi.com/Motherboard/MEG-X570-GODLIKE/Overview (has 3x PCIe4 x4 M.2 slots and RADI0 support for them... although doesn't mention if it can boot those. One of these can though: https://estore-highpoint-tech.com/collections/ssd7500-series-pcie-4-0-nvme-raid-controllers/products... - and has an advantage of raid 0+1 )
SSD has me head-scratching - size seems to change performance, so if I want 2TB modules, it looks like one of either:
Corsair MP600 PRO 2TB
Samsung SSD 980 PRO 2TB
WD_Black SN850 SSD 2TB
I don't need a fancy GPU, so I'll probably get a used 2080ti or similar for now.