I wouldn't waste the ber's,rather I would shop around for Silence runes. HEre are the stats:
Silence 6 Socket Weapons Dol + Eld + Hel + Ist + Tir + Vex 200% Enhanced Damage
+75% Damage To Undead
Requirements -20%
20% Increased Attack Speed
+50 To Attack Rating Against Undead
+2 To All Skills
All Resistances +75
20% Faster Hit Recovery
11% Mana Stolen Per Hit
Hit Causes Monster To Flee 25%
Hit Blinds Target +33
+2 To Mana After Each Kill
30% Better Chance Of Getting Magic Items

Otherwise I would go for a 5 Ohm 1 Um phase blade.