I took a look at the clickies of the following:
1.) Powerful Metal Legs = Form of Endurance VI (+HP clicky)
2.) Powerful Chain Legs = Form of Protection VI (+resists clicky)
3.) Powerful Leather Legs = Form of Endurance VI (+HP clicky)
4.) Powerful Silk Legs = Form of Protection VI (+resists clicky)
I think Leather and Silk are just fine as they are, but...
Powerful Metal Legs have 3 tank classes that can wear it, wouldn't it better if it was an AC clicky instead (ie. Form of Defense VI)? Also for chain, 2 of the classes in it are melee classes (or 3 if you count the ranger) and would likely be eating ramps... perhaps Form of Endurance VI might be more useful here?
Just my 2cents.