I have this 486 motherboard that has a clock crystal. It came with a 50 MHz crystal installed, and a 486 SX/25 CPU, presumably running at... 0.5X motherboard clock?

There are jumper settings for 1x and 2x. It was set to 1x.

I upgraded it to a 486DX2/66 CPU and set the jumpers according to the manual below. When it boots it says the CPU is running at 50 MHz, and that it is a DX2. So it knows about the DX2.

It would seem like it's halving the crystal's clock speed internally before the DX2 doubles it again.

However, all of the pictures I find online of this motherboard show it with a 33 MHz crystal installed in the socket, which I would assume gets doubled directly by a DX2 CPU rather than halved first by the motherboard.

I'm a little confused as to what's going on here, so I ordered both 33 MHz and 66 MHz crystals from eBay. I'll use one of them, I'm sure.

Did I actually overclock my 486DX2/66 to 100 MHz with a 50 MHz FSB, running my VLB cards at 50 MHz too? The system runs perfectly stable so I would assume not, but then which crystal would I use to get 66 MHz, the 33 MHz one or 66?

Info and manual for my motherboard:
https://theretroweb.com/motherboards/s/fic-4386-vc-v
https://theretroweb.com/motherboard/manual/32520.pdf