BARD resource?

[Viridiana]

But if you want to get picky, since VB front loads 100 potency, you could use it first on any enemy that you'd expect to die in <12 seconds, and WB first on one that you'd expect to live > 12 seconds. As both skills would have done exactly 240 potency worth of damage at 4 ticks (12 sec)

I disagree. I did the math on it several months back, and it actually breaks down even more than that.