How did you do on yesterday’s photo of 3 foot strikes ?
Now, look at the women ! Almost pristine ! Still a little evidence of cross over gait in each of them, but pretty darn good ! The feet are falling under the body mass, not good for sprinting, but utilized more in endurance athletes. If you have enough abdominal and hip frontal stabilzers (ie. G. Medius et al) you can play safely with the efficiency factor. If you do not have the strength, you sacrifice efficiency and risk injury at multiple sites in the lower limb. The more cross over you have, the more the foot will strike in inversion (more lateral foot strike), then you much hope you have enough gluteus medius strength at the hip, medial knee stability strength and ankle/arch strength in muscles like the tibialis posterior. 

Kara Goucher and Shalane Flanagan, right, shown here leading the 2012 Olympic Trials Marathon,
Photo: Kurt Hoy/Competitor