Now this is a topic I can get into.
I am a game collector and love digging out my old copies and reliving my younger days.
I have an older Pentium 400 that I use to play all my old DOS games on. I dual boot between DOS and Win 98. If I boot to DOS I can run Win 3.1 from there and I have an emergency disk that I can boot to Win 95 from if needed. (Yes I actually ran into a Win 95 game that would not run on 98.) When I need to slow it down I have found Moslo does ok with a little experimentation. I just got done playing Ultima IV and had to run Moslo set at 2%. Worked very well for a game created in what, 1985?
ISA is a must. The trickiest situations I have run into involve games that do not support expanded memory and must have the drivers load below 512/640. I have found some downsized mouse and CD drivers that have been invaluable.
I installed both a 5.25 and 3.5 floppy because many of my earlier games are on 5.25 media.
Good luck. My Geezer machine has been more valuable than my newer XP. I think I need to start building a backup.