I would choose one with Intel BX chipset. You won't regret choosing it, unless you love to play with drivers, BIOS and chipset tunning 😀
They are just solid - rock stable and top performance. Build and work/play. Someone may say they're boring - not much to improve.
For CPU - faster is better. P II 400MHz has 100MHz (compared to 66MHz for 333) what is also important.
For speed sensitive DOS games P II 333 is already too fast (Runtime Error 200 occures above 200MHz), so P II 400 is better.
On my PII 400 with GF4MX440 (64bit) i can play Quake 3 and Half Life 1 in 1024x768 resolution with 50+ FPS.

Between two BX boards you mentioned - Soyo board probably will be more flexible than Intel one.

As long as the caps and condition look good I'd go for either of the Soyo boards, depending on what goodies and features which board has that you would like to utilize.
If you just want simplicity and reliability the Intel board is hard to beat. No bells and whistles just solid.

I also recommend one of the 440BX boards (although I never had one, the Soyo SY-6BA+ looks like a nice, solid board).
Now, regarding DOS gaming... this is one deep rabbit hole 😀 Games that are not speed sensitive (especially late DOS games) will run fine on such a PC.
However, there are some DOS games out there that have issues with fast CPUs (and the term "fast" can mean a lot of things 😀 ). For example, some games literally expect just a certain type of CPU, like a 386 DX-25 (not slower/not faster). Some games run too fast with a faster CPU, other games have sound initialization issues, etc.
So, having said that, what you want is to have a very flexible PC, where you have very granular speed control. Unfortunately, a P2 400 on a 440BX is far from being flexible. It's either very fast or extremely slow (286 equivalent speed when you disable the cache). A faster CPU like a Pentium 3 Coppermine 1 GHz would be better in this regard, since with disabled caches it would reach a 386 DX-33 equivalent speed (which is a better all-arounder). Still, there are other platforms out there that are better, since they offer a lot more flexibility.

I'm putting a vote in for the Intel board.
BX based motherboards are famous for their stability so you can't really go wrong what Intel lacks in flexibility it makes up with even better stability.

zyga64 is right on the mark re CPU. Go with the 400Mhz as anything broken on this will still be broken at 333Mhz.
If you don't own the CPU's I'd go faster still, My 600 plays all my 9x games that don't work in XP perfectly and vast majority of dos games still work (the ones that don't would still not work at 400)
and faster still Slot 1 CPU's aren't that hard to find.
If you do have the CPU's though, I'd try it out first and see if you really need the upgrade, that's the great thing about Slot1, quick easy upgrades

another vote for BX, as for the CPU - if running games up to 1998 I don't think it will matter much between 333 and 400mhz in terms of your gaming experience

what about the rest? which OS are you planning on, how much RAM and storage and what video? sounds like a nice project to me

gerry wrote on 2021-06-15, 13:37:

another vote for BX, as for the CPU - if running games up to 1998 I don't think it will matter much between 333 and 400mhz in terms of your gaming experience

Probably not, but the 4x multiplier means you can run the 400 at 266MHz, where you can't clock the 333 down, so it's marginally better for older stuff (although still much too fast for really speed-sensitive things).

Note that you might not be able to change FSB on the Intel board, which could be a reason to go for the Soyo BX board instead.

Early Pentium II 400 with the dA1 stepping have downward unlocked multiplier, you can easily run them at 133mhz if needed. Same for the P2-333 with dA0 and dA1 steppings. With L1 cache disabled at 400mhz, it's about the speed of a slow 386, which is also appropriate for some early 90s games. Unless you have a bunch of late 80s and early 90s DOS games you want to play, I wouldn't worry much about the speed sensitive games.

gerry wrote on 2021-06-15, 13:37:

another vote for BX, as for the CPU - if running games up to 1998 I don't think it will matter much between 333 and 400mhz in terms of your gaming experience

what about the rest? which OS are you planning on, how much RAM and storage and what video? sounds like a nice project to me

Hi, thanks for your response.

At the moment I will only go for the mother since here in Argentina it is very difficult to get these pieces and I have found these models by luck.

Regarding the S.O, it is probably win 98 S.E. Video, I dream of a Vodoo 2 as a boy, I wanted one but it couldn't. But here there is only one but it is very very expensive. There are also some vodoo1 at reasonable prices.

Thank you all for your answers, I think I will decide on the mother Intel, I am looking for more reliability, I do not plan to make modifications, but to try to keep the equipment as original as possible for its time.

I tell them that it would be the second project that I Build. The first was an Amd k6III that I finished building a few years ago. It consists of an Asus p5a motherboard and an Asus Geforce 3 Ti 500 deluxe among other things. I'll upload photos of that project.

Thanks again.

Good to know about the dA1 PII 400, one of my computers was PII 350 and had lot of fun with it but the processor was locked.

Cheers,

Voodoo 2 cards are not what I'd call cheap anywhere anymore. At least on ebay or places like that.
You can still find them on local trading sites, markets, places that people use to simply sell old stuff they no longer want.
It'll take time and luck as these people don't actually know what they are selling, for them it's just a old computer.

If the Voodoo1 is a good price I'd still grab it. They have also gone up in price and still sort after as have better dos compatibility.
You can also keep an eye out for the 3DFX Banshee it's often overlooked but I was playing Need for Speed High Stakes on it just fine earlier in the year.