I have mixed feelings about armor as DR. I haven't used it, thought about it for a long time, discussed it on these forums, and changed my mind serveral times
Usually the reason why gamers want this variant is realism. However, the numbers they come up with are usually not more realistic than just having armor as AC.
For armors such as Leather/Hide and Natural Armor, it could make sense that they provide some DR. But an armor made of metal should provide a HUGE DR to be realistic. It would take a heroic strength to hit someone's breastplate and hurt him at all.
Monsters and PC are supposed to be heroic, but IMHO a DR 5 would be balanced game-wise, but is not realistic at all, because it means that a low-level character still hurts the guy in plate mail with many normal weapons. You could say that it is realistic on the average, but in that case why not sticking with AC?
OTOH using DR means to have the problem that certain weapons are completely unable to damage the armored opponent, even if the armor does not cover much of the target. For this reason, I'd prefer that DR would be applied to Natural Armor, which typically covers everything, but not worn armor.
But if one wants to use such a variant, at least I definitely suggest the Iron Heroes RANDOM DR, because that does not have the weapon problem at least.