2 amber archon shards: cast speed.
3 crimson archon shards: strength.
137% strength is needed with [Corrosive Projection] to fully strip armor with Terrify.
With 2 Tauforged crimson, you can replace [Power Drift] by [Cunning Drift].

Arcane Pistoleer is open slot, I'm playing it with Pyrana Prime, but it could be Molt Augmented if you want to slot something else for instead of crimson shards.