I've been doing a lot of walking lately. It's pretty hard to exceed 4mph, even when you are working yourself hard. To get up to speeds of 4.5-5 mph requires a special movement technique. Walking athletes call it "power walking", and the British military refers to it as "tabbing". Basically, you need to throw your hips forward each time you take a step - thereby lengthening your stride by a few inches. You can train yourself to do it. It still counts as walking because your heels hit the ground before the ball of the foot ... but the average spectator might think you were almost jogging.

I would agree that a steady pace of 3 mph is more practical for the vast majority of people, esp. over varied terrain (but with solid footing).

Pete 2