As far as optimum gradation, i'm not sure. But I believe the typical state road ABC stone (or GAB depending on where you are) was what came to the site on a couple of projects I've worked on. I couldn't open the specification page but these were the guys.
A common material used in the Pacific NW is 1-1/4" to 3/4" clear crush. This has also been called a Railway Ballast. It is important that this is a clean material with less than 5-percent passing the #200.
Work with your local contractor. They are very good at providing information not only on what is best for them but what materials, locally, are the best. They are often happy to help by knowing about the job and by having a bit of inside information about the tender.
