I tried searching but didn't find any info on this so I did some testing myself. I dunno if this is already present in the boards somewhere, anyway just sharing. I took a hex editor and noted DR change with light armor and heavy armor skills. quality of armor seems irrelevant as long as its the appropriate type. anyway here are the results (I omitted the levels where there was no change in DR):

Seems like DR from Light Armor is 30% LA for Head, 30% LA for Torso and 20% LA for Legs, always rounded down. For Heavy Armor it seems it's 50%, 50% and 30%. Looking at the table you get the best DR per point ratio every 10 levels for both skills.
Also, hoping a Skill Effects thread (similar to the Stat Effects thread) is put up.