I ride crushed limestone with my steel Trek 520... on my commute and I do not think you will have any issues. It is actually a pretty smooth ride and the steel soaks up any bumps. The only time it is a bit more bumpy is after a big rain.

I can actually cruise pretty fast on the limestone section of our MUP. The only thing with this surface type is all the whitish dust the bike collects. It gets pretty dirty so , I find myself cleaning the bike and drivetrain a lot. If you have fenders it will cut down on the dust though.

Let us know how the test ride goes... Sounds like a great ride if you decide to go.