Hey there!
I am using a K6 350Mhz on a board which seems to be the one attached as PDF.

This Manual does not mention a Turbo Mode at all. However, it does have a Turbo LED (Pin 13 and 14)

I got an old case with:
A Turbo Button
A Mhz Display
A HDD LED

Now Obviously the Turbo Button won't do anything if its not connected and I can't connect it as there are no pins for that.
The MHz display (for the turbo) is also somehow connected with that turbo button. So...alright, I am leaving that out as well, just for now.

However I saw in this video here: https://youtu.be/zpq9irl2yE4?t=552
That some boards do have a turbo mode when pressing ALT+CTRL and +/-.
I am using Symantec System Information to check the CPU speed as shown in the video, and upon pressing ALT+CTRL+- the CPU score goes from 180 down to 51 (neither value makes sense, but at least you can see that something is happening).
So it does seem like this Board does have some kind of "Turbo Mode".
And I would assume that if the status is changed the Pins for the Turbo LEDs would show a different signal. Which is where the HDD Led comes in, which I "abused" for now by connecting it to the turbo pins, assuming that it should either be On (if turbo is on) or off. But depending on how I connect it to Pin13/14 it is either always on, or always off. The status doesnt change when changing the speed.

But shouldn't it? Do I misunderstand the Turbo LED headers?