User blog comment:KillHil/Got Questions for Gearbox about Borderlands 2?/@comment-2005959-20120319171105/@comment-2005959-20120321002134

ultimately, i find that the only most challenging playthrough balance is PT1 vanilla => DLC1 PT2 => DLC3 PT2. this method plants the player at or just under the level of the following DLC's baddies. unfortunately (or fortunately dependant on your perspective) this leaves little room for challenge in DLC4 even with grinding kept to a minimum.

(current build is untouched by WT/HexEd)