600 damage from WOD, is that a cap? does it not really kill things at 30% health? or is that the damage if they are above 30%?
The cap for WoD is only limited by how much SDI you can fit on your suit.
The base damage for WoD seems to be 300 (at least in my experience)
You can get 100% SDI from your suit, which makes it 600.
Then there's additional damage increase from reaper form and arcane empowerment, which varies based on your skill and the level of arcane focus. I don't recall the numbers off my head and most places you'll look it up are wrong, so we'll call it about 30% for the pair (my max = 600. Without AE and RF = 452) which puts the max up above 780 points of damage.
There's also a rumor going around that certain slayer books (elemental)work with WoD on certain monsters(Dark Father), but I haven't tested it so I won't mention that further.
The problem there is that it's very impractical to make a suit with so much SDI and still have it functional as far as resists, LMC and LRC goes, which are all pretty important to a tamer. So most folk's WoDs will be less powerful than the theoretical max.
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Edit: and the damage done to a creature above 30% health is insignificant. It's comparable to a fireball in most cases.