Silver Sword upgrade, is it worth it? Options

[Jon Irenicus]

I was wondering if upgrading the silver sword to the diamond sword +4 was worth the materials and the cost.Does the vorpal effect has chance to kill tough enemies?Or will they be immune to death effects like that?I would like that people that already played through the IA with that weapon could offer their opinions on its worth.Thanks in advance.

[Shadan]

Personally I would buy Warblade +4 and forge Warlord's Blade asap. It's immunity to charm and confusion is crucial, and thanks to god, I chose 10 % weapon resistance wich is very valuable also. My F/T dual uses this sword when he needs imminity or weapon resistance, and I am using Staff of the Ram or Poseidon's Wrath when he needs higher damage output.
Regarding instant kill efects: My blade is using Axe of the Unyielding+5 now (among many other weapons ) and those instant kills are quite rare... There is a saving throw against this effect, it's proc is lowered etc. Not totally bad, but if you are low in gold I would chose Warlord's Blade...