Vray 3.20.02 Environment Fog

Inside the gizmo

Outside the gizmo

Near the gizmo - Render time on my machine 1:14 minutes

I always forget how to get the Vray Environment Fog to render somewhat quickly so I thought I would post my settings here so I can find them.  I think the main things is that the steps should be about 1/3 the distance.  

My gizmo is 6000 x 6000 x 3500 units. My units are in Feet

I used a noise for the density.

From the side