I see a lot of people thinking that the Carnevil/Zuni build is the fastest, which I just don't think is true, as you're missing out on Manajuma's and the 150% movement speed Angry Chicken. Here's the build I've developed.
The idea here is to just kill yellow/blue packs for their DB, and T8 is pretty optimal for that. You get a guaranteed Death's Breath from elites with the 5% chance for a third at this level.
The gist of the build is that Helltooth's 2p, 1500% wd/second Necrosis does a boatload of damage even without the 6p bonus. Firewalls with Jeram's Bracers also do a ton of damage. Necrosis and Firewalls buffed by F/R, Grin Reaper, Furnace, and Harrington Waistguard then do even more damage that is enough to take down elites on T8 quickly. Manajuma's can then also be used to get ridiculous Angry Chicken movement speed in between packs.
Here's the general rotation of skills/movement: Pop into Angry Chicken, run around opening chests (for more legendaries and to activate Harrington Waistguard) and explode on any elite packs you find. Immediately go into Spirit Walk to gain invulnerability, throw a jar of spiders and
zombie bears Acid Cloud (for F/R activation,) then spam your Firewalls. It should not take more than two activations of F/R (usually just one) for the elite to then be dead. Turn back into a chicken and start over.
For more detail, read below:
To be fast, we use the Manajuma's Way set for ridiculous speed in running between elites/champs and pretty much ignoring trash (to keep uptime of Angry Chicken high.) We also use Soul Harvest - Soul to Waste for a lengthy and spammable increase to speed and intelligence.
The damage from the build mainly comes from Wall of Death - Firewall. The 2p Helltooth applies Necrosis with your Firewalls and gives you 50% damage reduction with the 4p bonus. Jeram's Bracers allow you to stack up your Firewalls quickly, and for 100% increased damage. Zombie Bears and Corpse Spiders are for activating your Focus/Restraint to further increase damage. Grin Reaper mimics and Harrington Waistguard similarly increase your damage. These damage buffs, along with the Furnace in the cube and the gems we're using all make fights against yellows/blues take just seconds.
There's a ton of room for variation in this build. If you find you don't die often, you can drop the 4p Helltooth and run something different in the shoulders, chest, or pants pieces. Grin Reaper can be swapped with any of the Sage's pieces (head, gloves, boots,) and you could wear something like St. Archew's Gage for a giant shield, or Gloves of Worship if you think that's more useful. The belt can also be swapped out for a Goldwrap, and the third gem changed to Boon of the Hoarder, which would give practical invincibility and a buff to movespeed.
Video of the game play has been added since people are more interested than I'd anticipated. I'm using an Esoteric Alteration as my third gem since I was lazy and hadn't swapped it out, and I'm also missing 13% movement speed from paragon since I'd forgotten to redistribute those after I got a new pair of boots. The map is nice in that it has a lot of chests to proc Harrington, but the elite density was just average. Overall, I got 41 DB within 6 minutes, which is about 410 DB/hr.