My understanding is that the Cyrix 5x86 is pretty much the fastest option for non-Pentium processors - frequency dependent of course; if you get to the point of massively overclocking the AMD X5 or P24T things change. The P24T overdrive has somewhat higher FPU metrics as a ratio to clock frequency but is limited in outright frequency it will run at.

There's extensive data in this thread: The Ultimate 486 Benchmark Comparison

With 4DPS you need to use FPM RAM, not EDO. EDO will not work and will cause funny error messages on boot (weird sounds with different pitch on pc speaker included)

Thanks I forgot all about the EDO memory thing!

To be honest there doesn't seem to be much that is expensive (for how much fun I will have with it over my AMD DX2-80). Will a AMD DX4-100 offer much of a performance increase beyond the MHz (e.g. cache).

As an owner of a Cyrix 5x86... I'd recommend the AMD 5x86 133. The Cyrix part can be faster than the AMD part, but it requires some luck to overclock the 100MHz part to 120MHz, compatible boards (which you have) and perhaps more importantly, some degree of tweaking to enable features and registers that are disabled by default. Feipoa's research and work on the subject is nothing sort of amazing. By default, I find the Cyrix parts to be somewhat underwhelming, but they can be faster. Unfortunately, even with a lot of tweaking at 120MHz, my system is not meaningfully faster than AMD's 5x86 at 160MHz I would say. I can hit 17fps in Quake's timedemo though, that's cool 😜

Perhaps I'm looking at it the wrong way, but AMD's 5x86 133 is more readily available, at a lower price, has greater compatibility with motherboards since it's really not much more than a higher clocked 486, and overclocking to 160MHz is more or less guaranteed as far as I can tell from users around the world. At that speed, it's blazing fast for a 486. The Cyrix part is not worth it IMO, unless you're not adverse to spending a lot more time to tweak things and make everything stable.

The Pentium Overdrive can certainly be a lot faster for 3D games. IMO a bit less interesting since it's really a Pentium on socket 3. Also more expensive 😜