Purge level 3 and 4 i hate them becasue there start enemies with explosive orbs that can be devastaed for thralls.
As minimum preparation for that levels of purge i suggest cimmerian warriors III and if you have possibilty, cimmerian berserkers, all aquired in mounds of the dead area. Also as cheap but good equipment for them i suggest full cimmerian heavy armor and starmetal 2-hand weapons dropped from all cimmerians there.
Six cimmerian warriors III with that gear placed close each other with few stack of basic gruel food make them strong “power wa;;” against tier 3-4 purge.