I would say that the intel would be the slowest here. The reason is, at least I think, that it has the lowest transistor count - AMD version came up later, so that the could have added some more stuff into it. More transistors = more power when overclocking. Cyrix has a certified 486 core from intel too, and since it is on higher clock, wins, EVEN if it is from this company...Beware of the DLC and SLC, those fake 486cores. I may be wrong, but I'm writing this spontaneously, so if you browse the net, looking for the trans. count, you'll get your answer approved by google 😀...

I don't know where you got the information you remember shodan, but I think its incorrect.

AMD produced Intels 486er in licence and they were identical, also clockwise. (until the last revision with WB Cache, but thats not asked for here).
Then there is no 486DX-25 from AMD, they entered the market with the 486DX-40.

As for the Cyrix 486, it is the result of reverse engineering and the core is a bit slower, but cache algorithm is a bit better. So it depends on the application. Though if you have a 33 MHz version it is probably faster than a 25 MHz Intel one.

Yep, Elianda's right - the cyrix core is reversed engineering, though I have to browse some of my HW books for the AMD version details...will post later.

As far as I know the performance between AMD and Intel 486 should be pretty much identical. While AMD did debut with 40MHz, according to Aad Offerman's chiplist, a 25MHz part was available.

I have heard that at the same clock speed the Cyrix 486 is slightly slower than intel, but no more than 5%.

Cyrix's 486SX on the other hand is a different story. That one only has 2kb internal cache.