I haven't tried this myself, so it's friend-of-a-friend info at best - but word has it a tier 3 NPC settlement can be taken with a force of 1x L10 Balrog, 2x L20 Dark Priestess, and a damage dealer force of 4x L80 Dark Elf and 4x, say, L80-100 Warlock. The Balrog should serve as a tank and the Dark Priestesses should pack enough healing power for everyone to make it out alive.

If it works, I owe Tomek a resonance stone and a bounty of ashen stone and/or prismatic glass ^^ But it will be some weeks before I can field that kind of attack force.