I have noticed that the break DC table is missing anything regarding materials stronger then Iron (like mithral and adamantine).
Iron Door is the biggest DC (28). I wanted to suggest expanding that part of the table with a lets say +2 DC if the material is mithril and +5 (or +10) if it is adamantine.
Something similar was done for Hold portal and arcane lock and I feel it should be done for these two materials as well.