For those of you that can afford it, a cold aura or defense aura merc from act 2 equipped with doom runeword would help bring down enemy defenses to cold.
Hel + Ohm + Um + Lo + Cham
Axes, Hammers & Polearms only
5% Chance To Cast Level 18 Volcano On Striking
Level 12 Holy Freeze Aura When Equipped
+2 To All Skills
+45% Increased Attack Speed
+330-370% Enhanced Damage (varies)
-(40-60)% To Enemy Cold Resistance (varies) <--- oh yeah!!
20% Deadly Strike
25% Chance of Open Wounds
Prevent Monster Heal
Freezes Target +3