@ Matt
After studying material science, I can say that the only difference between cast iron (2.1-4 percent carbon) and an even "higher" carbon-iron material is the difference between ductility and brittleness because of interstitial spaces being filled by carbon atoms. What makes a good
cast iron skillet is thickness which allows the skillet to store enough thermal
energy for sauteing and searing (not boiling from thin walls), smooth polished cooking surface, and
lack of impurity metals. It is possible to have trace amounts of lead or cadmium.
I know that Lodge Cast Iron cookware tests their metal quality, and a bonus they are made in America. Their
prices are very reasonable, but my only complaint is that their casting process produces a semi gritty surface that takes a couple years to wear down unless you grind it yourself (recommended). Dont be fooled by expensive gimiky cast iron products, the material works the same way so buy according to your preference.
http://www.youtube.com/watch?v=MgTKTh1UfiU