There're some games that were very ambitious for the time (or poorly programmed) that were never intended to be played at 30 FPS (or more).

For example the original Mechwarrior becomes almost unplayable if you go beyond 15 frames because you are probably expected to be an IBM XT user. Enemys will kill you before you can react at 30 FPS.
Today we think of 30 FPS to be the absolute minimum to be considered smooth but back then it was apparently accepted to give up a big amount of playability to feature polygons.

There's probably little you can do in these cases other than finding the perfect comprise of cpu circles for your setup.
I'm asking anyway what else you could do to make those games a little less painful to play 😀