Lawbringer for Act5 Merc

[Mikedok]

What is best sword to make Lawbringer runeword in for an Act5 merc?  Based on known damage ranges and weapon speed of base weapons, it seems like a ethereal legend sword would be the way to go.  But I heard a rumor that Act5 mercs get a damage bonus with one handed weapons.  I don't know exactly what that bonus is or if it exists at all.  Does anyone know how that bonus works?  And if you do, what sword I should be using for this?  Thanks.