I have in my 386 a SMC 8013 EWC network card along with an Adaptec 1542CF which the documentation state can be run at 20mhz on a t bus.
The late 80's cards very early 90's were designed for the 286 AT bus being able to go way faster than the standard 8 mhz. I am curious and remember
reading that the ATI VGA wonder can function on a higher speed AT bus as well. I haven't been on the site in a year and wonderous things have happened.
The PC Chips M321 board chipset was determined to be an OPTI 82C392 and the Mr Bios motherload has been found. Got to dig her back out. Kinda sad
that it wasnt the opti 82c495 as that chip could handle 50 mhz bus since it was designed for VESA bus at 50mhz. Wanted to get the 486 cache interleave going since it detects
the 486 slc. Wanted to do the 486DXr2 and set it for single clock at 50mhz with the board. best could be has for the ISA bus would be 20 at divide by 5 with a 100 oscillator
thrown in. This years project.

There are multiple versions of this motherboard - some are good, some not so.
You can find few more threads about it if you search around.
I happen to have two different versions of it - one good and another not so good.
While I like the good version a lot, it does not overclock well. Barely ticks at 45mhz, let alone 50, or above.
If you want fast and stable 50mhz+ look for sis (rabbit), or symphony based boards.
Personally I was not able to run the sis chipset completely stable with fpu, but other members here seem to be able to do so.
Opti 83c495x works stable at 50mhz+ but is clock-to-clock slower than sis and especially symphony. If you get a vlb version of it - graphics perf will be great.

The Cyrix DRx2 chips cannot be set to single clock mode. They default at 2X and there is nothing to change that. What you need is a TI 486SXL2-50. That one starts up in single clock mode and can be switched to 2X with software.