I tested this just 2 nights ago. I did identical damage output at 31 and 32 (using maxed VoC). My defense rating was a tiny bit lower. It seemed like the damage I took was the same, but it may have been a tiny bit different. I see both sides of the argument. One, VoG cap was designed with and beaten with a lvl 30 cap. There should be no problem beating it at lvl 30. Two, why wouldn't you maximize your character's defense rating as much as possible? Unless you are getting some particular perk on another piece of armor. All that said, whatever lvl you are, if you don't die and are getting the same number of kills...who cares what lvl you are? Experience is much more important than the difference between 30-32.