There are actually quite a few options for adjusting speed in DOS games.
In my opinion, the most flexible setup is Phil's 4-in-1 DOS machine based on a SS7, K6+. This computer can easily scale down to a 386DX33 all the way up to the equivalent of a Pentium II 450mhz. K6+ processors on an SS7 board are capable of disabling L1 cache in software, have an toggleable L2 cache on the board, and have a multiplier scaling from 2x-6x using setmul. You can even toggle between 60mhz-100mhz fsb for very granular speed adjustments, although only by accessing jumpers or dip switches on the board. The downside to this platform is that now, thanks to Phil, everyone knows about it, and boards in particular can be very expensive. Finding a board the is compatible with K6+ and larger disk drives can also be very challenging.
https://www.philscomputerlab.com/4-in-1-retro-gaming-pc.html
The next best thing IMO is a 200mhz or 233mhz pentium MMX with socket 7. The pentium MMX processors are a bit pricey, but you can use it with a lot more boards. The pentium MMX CPUs can have caches disabled and multiplier adjustments, but they can also disable specific instructions in software, allowing you to go as low as a 386DX25. The great thing about this setup is that you have a lot of control over the speed in the 386 and 486 speed zones, and it can go a bit slower than other platforms. The downside is that the pentium MMX is not fast enough for a lot of 3D windows games, you don't have access to AGP or larger drives unless you get SS7.
https://www.philscomputerlab.com/136-in-1-pentium-mmx.html
Another option is Slot 1 with a Via C3 processor. These processors can scale from a 386 all the way to a slow Pentium III (depending on the model) by adjusting multipliers and cache in software. The slot 1 boards are relatively affordable and support lots of features like AGP, DMA, and larger hard drives. Via C3 chips are a good choice for speed sensitive DOS, but their performance in windows is all over the place because of their weak FPU performance.
SetMul - Multiplier control for VIA C3 / AMD K6+7+8 Mobile / Cyrix 5x86
Finally, a real 486 platform can do a lot, scaling in performance as high a slow pentium with certain CPUs and motheboards, down to a very slow 386 or even 286. 486 board are hard to find, and not very convenient to work with, but it is an option.
Those are hardware solutions, there are software options as well.
Any slot 1 or socket 370 pentium III, and even socket 478 pentium 4s (and later I believe) can work with a piece of software called throttle. Throttle lets you use clock skipping to adjust the speed of your processor in software, down to as low as 12.5% of its normal performance. I haven't tried it with my p3 setup yet, but from what I have read you can reliably get around crashing and bugs in speed sensitive DOS games using it, and gameplay performance in a lot of games is more or less where it should be. Slot 1 and socket 370 boards also can be found with ISA slots for sound cards, are rather affordable, and have lots of features. A pentium III at 600-800mhz can get down to a 386 with l1 cache disabled, can approximate a 486 and a pentium with throttle, is great for early windows games, and they are very cheap. These boards also have lots of features like AGP, DMA, larger hard drives, USB, PS2, ect.
The downside to throttle is that it is not hardware control. From what I have read, clock skipping will get speed sensitive games to run, but you can still experience speed issues and inconsistencies.
http://www.oldskool.org/pc/throttle/DOS/
Finally, there is software like mo'slow and similar, that run a programs in the background to trip up your CPU and hog a bunch of resources in a configurable way. I haven't tried it yet, but from what I have read you can get your CPU to run very slow, but the performance is a bit erratic. Hardware based slow down solutions are really preferred.
Before you go crazy though, consider the list of speed sensitive dos games, and decide how important they are too you. For price and availability, any pentium 4 computer with a good PCI sound card will run lots of great DOS games just fine, is super cheap and has performance to spare for windows, will have lots of more modern board feature, ect. You can use throttle and often times disable some caches to get slow enough, and of course, there is always DOSbox to play some games you can't get to run on your hardware 😀.
https://www.vogonswiki.com/index.php/List_of_ … sensitive_games