I read this study a while back stating runners what the length between their belly button to feet to be greater than the length between their belly buttong to thhe top of their head. So, longer legs would be more desired.
So even though many east africans are short, the length between their belly button and feet are longer so they cover more ground with each stride than a person with the opposite body proportions with the same weight.
Also, the study said that this longer leg body cause the belly button to be higher up, which is the bodies center of mass, causing the person to fall faster(which running has a lot of falling since you fall with each step).
In general, This is why black people are fast runners and white people, usually with longer belly button to head lengths, are better swimmers. The longer upper bodies on white people help them ride on the wave they create while swimming.
SO, LONGER LEGS ARE BETTER
http://news.discovery.com/human/belly-buttons-sports-athletes.html
<-this is my source