i think it's a combination of the rider's natural comfortable cadence and how hard they are willing to push on the pedals. Your bike tends to decide your speed, not you. Let me explain; most people have a pretty narrow cadence speed range at which they are happy pedalling. Too slow is a slog, too fast gets manic. Now, if you have a fairly light bike with plenty of gear ratios, it's easy to find that sweet spot combination of cadence and effort. However, if you have a heavier bike with only a few widely-spaced ratios (Sturmey AW gears for example). the gears are further apart than your cadence "bandwidth". That means in order to get into high gear you have to thrash along faster than you really want, in order to get enough momentum to use high gear. If you get into high gear but your speed is too low, you're really slogging against the ratio. That means in practice a pootler will stay in their mid-range gear and let their cadence find it's natural level. If I compare AW gears to a 6-speed freewheel on the big chainring, L is roughly equivalent to 2nd, M is 4th, and H is 6th. However, my maximum comfortable cruising gear is 5th, the ratio of which on an AW hub falls roughly midway between M and H.