Well, I was right, the third beer was very persuasive and convinced me to battle on and check more machines.
However, I’ve not had much joy, with the next three machines all exhibiting video glitches. The second and third of those are, I believe, booting the diagnostics disk, but the screen image on two separate monitors is patchy. It’s obvious it’s at the same menu system, it’s just that it’s actually illegible.
I’m going to call it a night. I need to check whether the glitches are happening on the (now) known good europlus (motherboard 8237), as I’m beginning to suspect the monitor, monitor cable or even the PSU I’m using to test the machines with.
Troubleshooting where the issue is will have to wait for another day, though – probably after the weekend. At least I’ve gotten something done, so my conscience will rest easy tonight.