Ok, a CD/game that fails non-stop is this one:
Compilation Disc: CD32-350
Game: Mortal Kombat
Symptoms: "Insert disk into DF0" requester flashes on screen, goes no further.
Loads of the games don't work, but this is one that I've had a 100% failure rate with and have tried a million times, so using it as a "benchmark of failure".
Thanks for all your help too...I really do appreciate it and I'm documenting the lot so I can help others in future!