ARSENAL's a fine, fine piece of work. I'm using the Defense bonuses in my Scarred Lands campaign, not even converting all the way over to DR -- I'm trying to encourage the light, fast characters to stay armorless, more swashbuckler-y.
I'd reproduce the table here, but I don't want to take bread from other writer's mouthes. Just generally -- slow progression for spellcasters, good progression for fighters, darn good (but not insanely so) progression for rogues, bards, monks. One thing -- the DR's take into account firearms,so they do tend to suck up a heckuva lot of damage. A tweak downward may be necessary.
Have fun.