Per :
Also, the gravel in question is really just
crushed stone, easily 2" pieces and larger. It's not the typical
gravel you encounter on roads or paths intended for foot/bicycle
traffic, it's way bigger and deeper.

How much doe the stones more around as you go over them?

I've ridden my WTB Mutano Raptors (55/55 size) on what I call
"railroad ballast" a good bit with decent results.

My sense is the bigger the tire and the lower the pressure, the
better.

215# rider, tires at 35-40 psi.

But the stuff I ride on pretty much stays put as I'm going over
it. If the stones shifted around too much it might be a
different story.
--
PeteCresswell