Try to always have at least 2x the ar as your opponents defense for 75% chance to hit (minus block). The returns diminish exponentially the more ar you have vs. your opponents. So 6-8k is plenty fine vs 2k def enemies. But vs shouted opponents, exile using paladins (and their allies), and especially if playing with amp damage, I personally prefer 100% ar/life charms vs. damage/ar/life.