Since that motherboard uses the SiS 471 chipset, it probably relies on the De-turbo feature provided by that chipset. According to the documentation, the chipset can be configured to slow the system speed by either 1/3 or 2/3:

It achieves this by holding the CPU for a certain amount of time every 12 microseconds:

Not sure which of the two de-turbo speeds the ASUS motherboard is configured to use, but I guess it should be easy to determine that by reading the value of that register with a program like CTCHIP34 or some small custom program.

What I can say is that the slowdown with turbo is insufficient to be really useful for the things I want it for. I recall having some other issues with turbo on that CPU, too. Ended up going from Am586-133 to DX4-100, which is still fast with turbo. For my DX4, Doom demo3 full graphics does 41.6 fps at full speed, 15.9 fps with turbo, and turbo performance goes down to 11.4 fps with L2 disabled and detuning in BIOS. The third configuration was when Ultima VII got nice and playable.

I don't have parts yet to test this out myself, but maybe there is someone out there who is able and willing.

If the Turbo ON/OFF can be controlled by both software and hardware switch, does one override the other?
If the Turbo ON/OFF is changed by software, will a state change be reflected by the Turbo LED?

It might be helpful to regulate system performance in this way through a batch file specific to a program. It's probably even better if the Turbo LED status reflects the change.