Teh best Diablo Clone killer in the game is a Javazon like the one I posted some time ago in this forum.
You can find teh build in this thread:
My CS / Fury Zon (Viz's guide revised in a super-damaging PvM version)
If you are ladder, you can use an "Infinity" eth Cryptic Axe on your mercenary instead of the eth Reaper's toll. It has conviction aura when equipped, and it lowers the Clone's lightning resist by 85%.
Diablo Clone has 95% lit res: with Conviction from your merc, it becomes 10%. You also have a -45% lit res if you have a perfect gear (-25% from perf faceted Griffons, -15% from Thunderstroke, -5% from a perfect facet in the Stormshield).
So, when you face it, if you have my same gear (I'm rich in ladder, I know), Diablo clone will have -35% lit res.
This means that, with a fully (or nearly fully) synergized Charged strike, you are able to make about 55k + 35% = 74250 effective average damage per hit on teh Clone.
And since Charged strike is an ITD (= ignores target's defense) attack, you can pwn the Uber sUxx0r Diablo in about 10 seconds, or less.
Have fun.