Get a Costa Rica 300A.

They aren't all stable at 4.5 x 100. The one I have won't do it (retail SL32A).

IMO, overclock it for fun, but if you really need the extra speed, just get a faster CPU.

It's a 10% bump. Spec of that era is likely +/- 15%.
On silicon nodes the size of Manhattan compared to today's.
Today's voltages are barely 1/3 lower (~1.3v).

I wouldn't worry about it as long as the board's voltage is fairly stable.
Infact, if the caps are original, the extra voltage might simply be masking unstable caps.
If you really want to be safe, replace all the big caps near the cpu (usually 1200-1500 6v) and you might be surprised to see it stable at 2v.

I had an SL36A Celeron 300a that overclocked to 558 mhz (124x3.5) at 2.0V and it would even run at 600 mhz at 2.3V but unstable. A 100% overclock. It was legendary. Best overclock ever. I'm not sure if I still have that chip or not. It's been about 27-28 years ago. I remember I was running it on an Abit BH6 motherboard.

I think it's just the processor itself. The BH6 has been recapped, I can run my Deschutes 400 at OCd 126 FSB stable with 2.0v. It was fund to OC and use such a legendary CPU though and one off my list of things to do.

If I'm not mistaken, the maximum frequency in Mendocino is 533 MHz.

Therefore, anything below ~500 MHz is simply a mediocre processor one — just a big loss in the “silicon lottery”
133 MHz FSB for Mendocino is an impressive result (from 600 MHz CPU core).
The rest of the average results should be around 500 MHz.

mockingbird wrote on 2025-12-21, 15:11:

Get a Costa Rica 300A.

300A SL2WM (MALAY) is much worse?

ott wrote on 2025-12-22, 19:06:

mockingbird wrote on 2025-12-21, 15:11:

Get a Costa Rica 300A.

I have 300A SL2WM (MALAY), is it much worse?

Stepping was important when purchasing these processors at the that time—a preferable stepping means a higher probability.
At the moment, there are only two questions about your specific processor:
- Stable operation at an FSB frequency of 100 MHz.(Its the "classic" overclocking for Mendocino in thats time)
- Stable operation at an FSB frequency of 133 MHz (you very lucky, its result better then almost any P2 performance)

ott wrote on 2025-12-22, 19:06:

mockingbird wrote on 2025-12-21, 15:11:

Get a Costa Rica 300A.

300A SL2WM (MALAY) is much worse?

It seems to be a myth, both CPUs from COSTA RICA and MALAY are OK and acceptable for overclocking.
I tried to find any info about best 300A chips and everyone recommends their own CPU 😀

The fabs were never in either country.

The chips were cut from the wafers and put on the pin package there.

It is traditionally believed, and I tend to agree, that later processors have better frequency potential.
When the output of usable processors reaches its maximum, but supply contracts are concluded for low-frequency ones.
As a result, 533s are marked (programmed by burning fuses) as 300A.
Therefore, it is not the factory that packages the die that is important, but the date of manufacture.
That way, the chances are greater.