All enchanted mithril items are +4, chain mail and halfplate at least, I am fairly certain that all other enchanted mithril armors are too
Chongo,Your comment about going with dodge and DR for all ac reminds me of my PNP days. I spent a good bit of time playing under a system called "arms law" and "claw law." I forget what company made the system up, but it was pretty good. Your ac was Columns 1 (clothing) through 20 (full plate) and then you had a attack modifier based on your ability to evade attack. Each weapon had it's own attach table and different weapons were effective against different columns. For instances, a rapier could rip up someone who was column 1 but was relatively ineffective against column 20. If you exceeded a certain threshold on the column, it was a critical hit and you rerolled on the appropriate critical hit table (piercing, slashing, bludgeoning, etc.)Your attack modifier was a percentile that you added to your attack roll. The tables also had built in fumble results. The fumble threshold depended on the complexity of using the weapon. If you fumbled, you rolled on the fumble table and results could range from hurting a comrade, to hurting yourself or dropping or breaking your weapon.Overall it was a pretty nice system.