in my opinion the build will be completed with:
2 red tau archon shards (+30 PS) to complete de 400 power strength to complete pillage.
2 blue tau archon shards for energy (150 more + 225 base= 375, = having normal [Flow])
1 yellow tau archon shard for casting speed (37.5)

this build its useful in every thing you play with. maybe not much after level 250 or 300(in steel path)