[mmPzf]

I remember reading this. I also remember reading a compelling argument that the conclusions drawn by those studies were wrong, and that the actual cause for the difference in walking speed is age. People in big cities tend to be younger (due to urban migration, and whatnot), and with lower age comes faster walking speed.

I can't remember where that argument was made, and I never fact checked it, so take it with a grain of salt. However, it seems much more convincing than the 'pace of life' argument.