Quote Originally Posted by Necromas View Post
Zen archery is good, because you still get to run around in fullplate without hampering your casting or archery.
Armour doesn't penalise your archery or casting, but it will limit your dex bonus to AC, and if you're an archer you may have a decent dex and thus need some mithral armour to take full advantage.

Max dex bonuses for armour apply only to AC modifiers.