I was facing a puzzling problem with my 486. In The Lost Files of Sherlock Holmes, Case of the Serrated Scalpel, the introductory sequence where Holmes and Watson are talking always froze, requiring a restart. The usual area was just as Watson was reading Lestrade's note. I thought it was a speed issue, so I tried every slowdown feature I could think of, but nothing worked.

Then I decided to look at the manual, which was unhelpful. But I later thought that the reference card may have something to help me, and it did.

Note: If you are using DOS 5’s EMM386 expanded memory manager, and want to hear the digitized speech in Holmes, the default DMA […]
Show full quote

Note: If you are using DOS 5’s EMM386 expanded memory manager,
and want to hear the digitized speech in Holmes, the default DMA
setting of 16 will have to be increased. Support for EMM386 can be
achieved by adding the parameter d=40 after the EMM386 entry in the
config.sys file as shown here:
device=c:\dos\emm386.exe d=40
See your DOS manual for information about editing files.

Since I was using MS-DOS 5.00, this attracted my attention. When I added that line, the intro finally finished without difficulty. There are two other talking sequences in the game, and a crash at either of them would be very annoying.