Trust me, with kao's build (using a wizspike) you have major damage, but still have good resists. You need to consider that since hell be using bramble, he cant get cold & light resists from his armor.
hmm how about... the unique dagger that does -50% enemy's poison resistance. Remember that poison dmg doesnt depend on dagger's dmg... Also i guess wiz spike would be good too, but the unique dagger that does -50% enemy's poison resistance will kill enemy hell lot faster... IF you already have good resistance, use that. I hear they do like 16k poison dmg or something with wizspike i think.... not too sure about it tho =/