There is a thread on that but for the gargantuan only the big stinker work with loh and it's 100% per mob per tick.http://us.battle.net/d3/en/calculator/witch-doctor#hiTafU!ZbX!baYaca
The problem it seem to me with that built is you don't run vision quest. As far as I'm concerned anything that run bear or acid clouds requires vision quest.
Here is the built I'm currently using. http://us.battle.net/d3/en/calculator/witch-doctor#ifZUXT!ZUV!acaaYc
I have 6 mana regen from helm, 9 from off-hand, 9 from weapon and 2 from templar. The only thing that really matters is mana regen. With infinite mana you can pretty much stand there and kill anything and only have to move out of poisons and stuff that can 1 shot you.
You summon the bear before the fight.
You snare from far, pop spirit walk, fear and then idealy you cast 1 acid rain and spam bear. Spam acid rain as needed to keep 100% life. The bears are there because they do 3-5 times the dps of the rain and also because the dot part of the rain doesn't stack. This clears any normal pack in seconds with the right timing. For elites you of couse will have to kite but you can acid rain from very far to keep 100% healed and between the fear, spirit walk, the snare and the bear you can kite alot of stuff. I've managed to kill an invulnerable minion, fast, arcane, teleporter pack without dying this morning which honestly, before trying this built I would have tell you would be impossible to do or so.
The timing is about keeping everything down for VQ to be up all the time. Added bonus when you fear mobs into the 80% snare while spamming bear.
It kinda suck to have to destroy barrel with a cast of bears but that's the life of the WD if you ask me. Mana suck, vision quest suck as far as designed is concerned but it's too good to pass up.