So it identifies it as a 33MHz 486. But the speed is only comparable to a 15MHz AT (ie. a 286). The CPU's internal cache must be disabled.

Yeah, which would make you think "this must be a turbo problem" but damned if I can't see why it's doing it. I found something that I tried a little bit ago which lets you manually enable and disable the cache but it didn't do anything different with me "turning it on and off".

This is so frustrating!