Why not just check out SuperMicro's QVL guide for the board of interest. I picked an X11 board at random and looked at the QVL list, and they don't even stick to one specific manufacturer for the different speeds and sizes of RAM -- Micron, Samsung, and Hynix are all there. You could look at the Website of any one of those three manufacturers and see what they recommend for the specific motherboard. Maybe -- just maybe -- Kingston has its act together again now, but the company went from my first preference for RAM to my Never again list.
Pardon my ignorance for omitting, I did that. The Tested Memory List for the board in question list 3 results, one 2400 Samsung and for 2666 one Micron and one Hynix.
The Samsung and the Hynix cost north of 200 EUR and the Mircon around 100 EUR. Naturally i ran for the Mircon, but it's hard to get atm, so I was wondering if it "must be, one of the three"?
Edit: To answer my own question, I've found the answer in the Supermicro X11 E3 Resource , also thanks for the tip with the manufacturers website and searching in the hardware compat list. Couldn't find one on the Mircon website, but the tip to the Crucial comapt list from the other thread resulted in a newer dimm which is available here.
Sorry for the noise and thanks again.