Tank assasins in DPS gear doing huge damage is now pretty popular BS. Truth is, DPS specced assasins have a very low survivability, which forces them to utilize stealth and defense cds, but MUCH higher damage.
Deception specced assa is more of a 1v1 class with high burst and better stealth options.
Madness for sustained damage and decent cc.
Both destroy tank spec assa in dps gear if played correctly =)