Actually it is a pretty easy calculation and varies with each buyer. At some point the additional interest you pay over several years will catch up with the return you have on the principal you invest. Furthermore don’t forget to include taxes on that return you make. Also I believe the point of the original poster had more to do with walking away from the home then anything else.

If you freely admit that you can walk away from a home without care, then it is a no brainer to go FHA.