Just for fun - I clocked my "wonder walker" TWH mare the other day on our gravel country roads to see how fast she goes in her gaits. Her dog walk (quarterhorse speed) is between 3.6 and 4 MPH; her smoother 'working walk' is about 5 MPH; her preferred speed of running walk is around 6 to 6.3 MPH; and her faster running walk is 7.1 MPH. These are pretty smooth but on gravel she never goes as fast as she does on a well-worn trail, where I really enjoy 'riding the glide.'
By comparison, we have a foxtrotter too, and he prefers the running walk instead of the fox trot. When he moves out, he leaves us in the dust! So I know my mare isn't particularly fast, nor particularly smooth, but she is a joy to ride and has more 'gears' than I know what to do with.