It looks like defence from shields is only dependent on the size of the shield. I think metal shields should be superior to wooden shields but at the moment Breeland Militia has the highest shield-defence (9) if I remember right. I don´t think their shields are from high quality compared with the shields from Dragonslayers (shield-defence 8, altough it looks like a full metal shield and is pretty huge for a dwarf) At least in close combat the quality of a shield will/should be an issue. Or is the shield-quality somewhere else considered?
Apart from that this RC is awesome.