Andrie de Vries looks at average speed for different mens’ running events:
However, it seems that there might be two kinks in the line:
The first kink occurs somewhere between the 800m distance and the mile. It seems that the sprinting distances (and the 800m is sometimes called a long sprint) has different dynamics from the events up to the marathon.
And then there is another kink for the ultra-marathon distances. The standard marathon is 42.2km, and distances longer than this are called ultramarathons.
The analysis is done in R, and the code is available in the post. Check it out.