Unfounded opinions: Xeon-D in mini ITX but they are either expensive, Unobtainium, idle at way too high wattage, almost no expandability, too slow/old. Who needs that... Best to stay in uATX or ATX form factor. C236/246 with Coffee Lake Refresh Xeon would be good, UDIMM not RDIMM though. Bunch of slots, Fujitsu boards idle at next to nothing, stable. But either are boards expensive or CPUs are expensive or nowhere to be found. Not sure what happened with W680 chipset, also Unobtainium still? And more expensive DDR5 RAM. With Ryzen a board might say "yep, can eat ECC RAM", but nobody will be able to verify, if CPU really corrects and reports errors. Might change from one BIOS version to the next even. Schrödinger's ECC, just don't look. Bunch of irritating USB issues to boot on that platform. Who wants that... I looked into all this, because I wanted ECC and Xeon. Small. I looked very long... Settled on Asrock Rack 3647 boards with off-roadmap 24-core 8259CL Xeons. ECC works, idles at 50 watts with IPMI on, plenty PCIe slots. There should be a Thinkstation P320 SFF = small form factor. Maybe check those out. Wouldn't go smaller.