Theoretically, highest damage potential lies in Eviscerate attack. +100% per wound your target has. With enough wounds Eviscerate damage would be crazy. Obviously it would be hard to execute (no pun intended) because target would have to survive long enough.
I remember fighting The Beast and stacking like 20 wounds. There may be engine limit on number of buffs/debuffs per creature, but only devs know that (:
As for melee, maybe it's possible with: metal glove, pneumatic hammer, Heavy Fist, Combo, Taste for Blood and critical strike (with Cheap Shots).