I just dropped my gargantuan in favor of zombie bears, level 56, A2 hell. Running with: Poison Dart/Splinters, Acid Rain//Radius, Grasp of the Dead//80% slow, Zombie Bears, Spirit Walk//%life per second and Fetish Army//+3 little guys.
Running pretty safely for the moment, near the end of A2 hell. Loving the crowd control of grasp/fetishes on the champs, and mowing down the white mobs pretty easily with splinters/acid rain. Rolling when I'm with a tanky team, doing just fine on her own as well though.
Here's my build in act 1 inferno. It is a hybrid between Tank build and Zombie Bears build. I spam bears when I have lots of HP/mana, and use firebomb when I need to regen mana or HP. The DPS is probably about double a basic tank build on single target (the bears are that good).
Garguantuan's survival depends on your armor/resists. I am currently geared enough for my gargantuan to survive in act 1 inferno. Apparently the garg can survive well into act 2 inferno if your gear is up to snuff, but after that he will start having problems, even with perfect gear.
This is my favorite build that I have tried on WD so far. I timed a Butcher kill at 1 minute, which means it is probably enough dps to kill Belial before enrage (at about 14.5k DPS).
This build relies on a high Life on Hit (I have 950 so far) to regenerate HP using firebomb's dot.