asphalt flooring for barn floor

I'm putting up a couple more buildings, a 50×100 and a 30×200. They will be enclosed on 3 sides and have 25 ft wide bays. I've bought 600+ tons of asphalt millings for the floor and was going to put it 4 inches thick then compact them with a vibratory roller.

My question is do ya'll think 4 inches is deep enough or would 3 inches be fine. I am willing to use as much as needed but do not want to waste the millings if I don't need too. I've got plenty of Farm roads that could use some also.

Thanks for any info, I will be using these buildings for 3×4 big squares and I'm tired of using pallets.

asphalt flooring for barn floor