The higher damage main hand such as Azoth/Pharpe will definately benefit your weapon skills in the damage department, as well as gives you more umph as far as STR goes too. Just make sure you always have blau in there since the attack and accuracy bonus (not to mention the low delay thus amazing dps) are indispensable.
All I can really say is unless you got deep pockets and/or play dancer to 75, don't spend an arm and a leg for an Azoth over a Harpe. The evasion and acc bonuses do not justify it's price tag for a thief's use. Hopefully you get lucky on Xoltol that way you'll have a free 2nd highest base dmg dagger, first being Mandau of course.