A quick note on the DTK PEM 2500 motherboard: if you read the article provided by OP, they state the mobo is from 1990, because they looked at the BIOS copyright date, but in fact the product was selling in 1989 as well, as you can see from this ad on Infoworld : (https://books.google.it/books?id=czAEAAAAMBAJ … e%20386&f=false)
What happened here is that they designed this board a year or two earlier, and decided to keep alive the design to accomodate faster 386's, probably because the whole project was costly, and performance of the board was decent enough.
The board in fact can run a DX-33 (as you can see from this ad), but I think it's slower than a more modern board.
I'll take advantage of a rainy weekend, and make some benchmarks 😉.