It's interesting that your board has support for the 6x86-133. That's a pretty weird one, because it uses a very uncommon 55MHz bus.

The pictures of all your Cyrix chips are not the original 6x86. The first is 6x86MX which is based on the M2 core (later sold as Cyrix MII). The second two are 6x86L. They all use lower core voltages, which requires split rail like the P55C. I think if you use P55C voltage settings you should be fine.Just make sure your multiplier is set according to the CPU.
The 6x86MX is probably the way to go, since it has more L1 cache and is faster. It might also have better overclocking potential, and should support half step multipliers (1.5x, 2.5x, 3.5x etc).

Thanks for the insight. It's a tricky CPU range to navigate for the uninitiated. I'll start looking out for a good 6x86MX deal.

Pierre32 wrote on 2021-11-27, 01:50:

Thanks for the insight. It's a tricky CPU range to navigate for the uninitiated. I'll start looking out for a good 6x86MX deal.

2.9 volt MII-300’s were a pretty good bet
66x3.5 and 2.9 volts
Also fairly common speed grade.

Probably the trickiest part about Cyrix is all their dumb advertising jargon.
Originally the 6x86 didn't have P ratings. They sold at their actual clock speeds as 80GP, 90GP, 100GP, 120GP. They were actually somewhat competitive with Pentiums, so Cyrix got cocky and inflated all of their chip's perceived performance ratings. For example, 6x86-120GP became the P150+. Soon after this intel bitched at them because "P150+" tricked consumers into thinking they were buying an actual Pentium 150. So then Cyrix changed it to PR150+. I like to think of PR as the "Public Relations" rating system.
After everyone realized that 6x86 was better at frying eggs than playing Quake, Cyrix went split rail voltage and renamed their chip the 6x86L (for "low voltage" I think). Those weren't on the market very long because they ran cooler but still couldn't play Quake. So they got replaced by the 6x86MX, based on the M2 core. They talked about M2 for years, and on paper it looked great...but failed to deliver. MX was supposed to imply "MMX", but instead gave the impression of being low budget (like a Geforce2 MX). It was supposed to be faster because it had a lot of L1 cache, but still sucked at Quake. By this time PII was out and making the 6x86MX look really pathetic. Rather than going to all the trouble of designing a new product, Cyrix (Natsemi actually), just tried to trick people by renaming the 6x86MX to the "MII", hoping that technically unsavvy baby boomers might mistake it for a PII when they bought a computer at Best Buy. Strangely, only the Cyrix branded chips got remarked as MII. The IBM version still went with 686MX, except for a few at the very end.
The PR system got even more brazen in the late 90s, with chips like the MII PR333 only running at a mere 233MHz. Of course by this time intel had already cracked 1GHZ, so it became impossible to compete even by inflating speed ratings. In the end VIA ended up buying them, and the MII was renamed the MIIv (v is for VIA). By this time MII had only reached 300MHz. Cyrix engineers actually had a few cool designs in the works, but VIA shitcanned it, instead renaming IDT Winchips as Cyrix III.

After Cyrix went titsup, Intel made it their mission to continue scamming people, starting with Pee4, RAMBUST and Itanic.

Anonymous Coward wrote on 2021-11-27, 18:38:

Probably the trickiest part about Cyrix is all their dumb advertising jargon.
but still sucked at Quake. By this time PII was out and making the 6x86MX look really pathetic. Rather than going to all the trouble of designing a new product, Cyrix (Natsemi actually), just tried to trick people by renaming the 6x86MX to the "MII", hoping that technically unsavvy baby boomers

My MII-PR233 ran the original Quake just fine
I bought Cyrix throughout the 90’s because clock for clock (ignoring PR) the systems were simply much cheaper

Sometime After the 6x86L the Cyrix chips started to run Quake much more acceptably at the same speed grade.
There were “rumors “ that the Cyrix floating point unit was so unbelievably simple that they found it could run asynchronous and faster than the main core.
Others have claimed 3D “games” use an extremely small subset of the same couple hundred numeric calculations repeatedly and Cyrix optimized one instruction for the very limited “Quake math” so the game would run.

Whatever they did later Cyrix chips could run Quake significantly better.
In my personal experience moving from the original 6x86-Pr200 to a MII-PR233 my FPS in Quake easily quadrupled (maybe more)
and Quake for dos was then playable.