Here's the rolling resistance page from Hamilton castor <www.hamiltoncaster.com/Portals/0/.../White%20Paper%20Rolling%20Resistance.pdf >
The larger the wheel diameter, harder the tire and better the bearing the easier the pushing. If you don't need to steer use ridgid castors if you need to...
We've been doing a lot of performer flying of late and we've switched from a standard Hall's / Foy's type of rig to human counterweight. You just have a one to one system with your talent on one end and your counterweighter on the other who simply runs up and down a ladder or tri truss offstage...