Vengeance calculation taken where?

[adeyke]

But the mastery type +elem% and lower elem resist% affixes both help, yes? (e.g. facet jewels). A melee sorc using Kingslayer runeword for vengence benefits potentially from all three elem masteries, yes?

Yes.

And certainly speeding up vengence or increasing the chance that you connect with it helps. Seems like a pretty awesome skill (but I've never really played with it, in all these years!)

Yes.

Kingslayer vengence is an oskill grant, right? So a baba could dual wield with a paly scepter of +3 vengence with it and actually get the +3 boost, right?

Yes.