Take this simple test and report your findings and what distance(s) you find to be your best in running:
Wrap your right hand around your left wrist at the end of the thick end of the bone. Try and touch or overlap your thumb and middle fingure.
If your thumb and middle finger can't touch you have a large bone structure.
If you thumb and middle finger can touch but don't overlap then you have a medium bone structure.
I your thumb and middle finger overlap down to the base of the fingernail or to the first joint you have a small bone structure.
For example I have a small bone structure (overlap to the nail base) and tend to fair better in the longer races (HM and marathon).