Frost DK w/shadowmourne vs other sub-par weapons

So where does a shadowmourne frost DK get beaten by a dual wielding frost dk?

Havok's call normals? x2?
Blood venom blades heroic x2?
Havok's call heroic x2?

At what point do you decide "Aight, I'm not gonna keep using this shadowmourne and I'm gonna re-spec to the dual wielding talents" cause with the 2-handed build you skip the 2 dual wielding talents to save 6 points for other talents.

Also I know you don't do as much dmg as blood or unholy, but you still give the 20% haste buff if your raid is lacking.

Got best weapon in game... chooses to dual-spec XS