The copenhagen study is one that stays with me. Over a period of 35 years, and ~17000 people, there are some interesting charts showing guidelines to optimise jogging for longevity.

If I recall correctly, the best benefit was for joggers to run three times a week for 7 kilometers at 7 kilometers per hour. This would give an extra five years of life, and as the parameters (#times per week, distance, speed) veered from this benefits declined along a bell curve.