I just finished a trip from Joplin MO to Glacial National Park, And back this july. I was pulling my home made trailer 2up 08 RSTD 8" wheels Total trailer weight with cargo 300 pounds. On the slab operated at speeds of 85 mph for several miles, But mostly at 75 mph. If trailer is set up right bearings set properly packed good loaded right, Proper tongue weight, Axles in proper location. Some would say any speed you got the balls to pull it at would be good. The better question is how much room do you need to stop at these speeds.