> Minimum threshold cause the monsters to ignore certain effects. For example if you stun a Champion for 1 second, it is reduced to 0.35 seconds which falls below the 0.5 stun threshold. This particular stun is therefor completely ignored.
Knockback effects are not reduced in any way, but you must meet the threshold for them to have an effect.
I could find no information regarding whether CC reduction is increased by level difference, but if it is then Normal monsters have CC reduction too. Again assuming it does, the Elites in Act 4 Inferno have the most resistances possible. If you …