In my opinion, the True20 damage system is broken.
I don't know if you already played it but I suggest you run some game before considering using True20.
You'll notice that PCs are virtual tank until they run out of luck point (it's not the real name but I can't recall the right one at the moment).
I run a one year campaign in True20, hopping for quick hack and slash combat. In reality, I got dull and boring fight, where a lucky toughness save makes you immune to anything.
I quickly ditched the system and put it in the pile of "good idea on paper, bad implementation" stuff.
W.