Alright get ready for a giant post guys....
I'm going to argue that for this challenge the party composition for us barbs is going to be:
Pure Support Monk
Pure Support CM Wiz
2 HotA/Rend Skorn Barbs
Support monk does not need any DPS whatsoever and will run something similar to:http://us.battle.net/d3/en/calculator/monk#aXVfgk!afU!YYaZba
But for the uber set this setup should be used instead:http://us.battle.net/d3/en/calculator/monk#adVfgk!afU!Ybacba
Depending on the gear of the party, dropping serenity-tranq for WotHF-fists of fury to proc nirvana on the non-uber encounters may be the best choice.
The monk should gear for max APS, LoH, CrC, bonus to elites (for ubers) and some health globe bonus. Their FoT is going to provide ~0% of the party DPS and is mainly to gain the spirit to be supporting through 20% guiding light, 48% overawe, 12% flesh is weak as well as 20% dmg reduction for the party (CS-implosion is GREAT for proccing this).
Specifically for ubers, a 10%+ bonus to elites sunkeeper will be required. EP scales off of non snapshotted bonus to elites and "enemies take X% more damage" skills. With the party composition I'm suggesting this will be 20% (base) * 1.40 (bonus to elites) * 1+(48% overawe, 12% flesh is weak, 20% time warp, 15% bone chill, 10% conflag) = 57.4% of HP in an explosion.
MP10 4 player Kulle has 345M HP, meaning the explosion will deal 198M damage to SB. SB has 517M HP which means 172M more than Kulle. If we manage to get a double HotA on the two, Kulles death should result in death of SB as well (that the monk should serenity to avoid the 10s death penalty when it would inevitably die from the reflect). The same is true for Rak Ghom.
For the farming portions the CS is vital to getting good DPS from the barbs. Barbs should be running lacerate which isn't the best range, but CS should pull the mobs close enough to Lacerate and HotA. Getting EPs off on the lower Hp mobs will also help take down the higher HP mobs.
For elite specific cases, the EPs and CSing become even more important since HotA has a pretty small hit box. If you can set it up so that the HotA barbs can hit 2 targets. The death of those two targets will deal 57*2 = 104% monster HP and kill the remaining mobs in a blue pack. Using this on yellow pack minions is a bit less effective, but still a good way to speed things up. With my current monk (check my profile) I know that I have enough spirit to be able to get the EPs off and overawe spam even on our super geared VotA farming runs where elites go down in ~5 sec.
Pure Support CM Wiz
The build would be something like this: http://us.battle.net/d3/en/calculator/wizard#VXYjgO!beg!YacaZZ
Which would provide 20% in time warp, 15% bone chill and 10% conflag (procced by sparkflint) damage to the party as well as gain better freeze with evoc and pinpoint. Since the DPS isn't that great going with crystal shell instead of shards is ideal.
The CM would gear with as much crit chance as possible while hitting 2.74 APS with decent LoH and ignoring crit dmg and avg dmg. We could get away with somewhat lower than normal LoH since the DPS of the CM is low enough that reflect won't be an issue. Also since we're dropping EB and SA the DPS will definitely be lower. Since we're dropping EB we can also save some gold by dropping down to 16 apoc instead of the normal 20 (I dunno if you can drop down to 10, would have to do some testing)
I know there has been some discussion about how CM wizzes provide pretty good DPS especially when combined with CS monks; however, in most of the time consuming situations that this challenge is involved in, there will be very few mobs on the map (ubers/bosses) in which cases CM damage doesn't scale nearly as well. In this case I would argue that having a CM with a very good freeze rate would be ideal. I mean we will be killing trash mobs for small periods of time, but I think 2 well built skorn barbs throwing out rends and HotAs with the +100% or more party buffs is more than enough to take them down fast.
In the above 2 cases we want to spend as little of the budget as possible. Since they're only in support roles they just need enough CM procs to freeze or spirit to cast spells and then EHP to survive. If we could get away with 500M or less on these guys we can really beef up the barbs with 1.5B each.
HotA Rend barbs:http://us.battle.net/d3/en/calculator/barbarian#aZPcRQ!YZX!bZcbYZ
We all know and love this build. It be slow but the DPS is the best output for barbs in stationary fights.
With a good CS, positioning and CM freeze, we won't need a -5 HotA soj to maintain bezerker rage since hitting 2 targets shouldn't be a problem except for Belial, Azmo and Diablo encounters. Also, one of the barbs dropping OP-KS for impunity to help buff the group. For the Diablo encounter, both barbs should be swapping out OP-KS for groundstomp to help the CM maintain CC lock on phase 2 of the diablo fight if necessary. I'm not entirely sure about Belial and Azmo atm since you won't be able to maintain BR even with superstition.
So why not a WD?
A WD definitely provides very good sustained DPS, party buffs and would be great for ubers in a snapshotted situation; however, this challenge is much more than just ubers so they fall short in a few categories:
1. The bonus from BBV and paranoia (most bosses can't be hexed) stack additively with the bonuses from the monk and wizard. Since we have +125% dmg already, the +50% from these two skills (which aren't up all the time...) only result in a net 22.2% dmg increase.
2. Getting a non-snapshot WD to attain the EHP and LS to survive the reflect dmg bursts (since you need to have EHP equal to 10% of your single tick dmg to survive as well as being net positive on mit vs LS) of SB will be very hard to do on a budget. It's very easy to do with a snapshot WD, but a snapshot WD (by this I mean like 4-5 pieces of gearswapping) would do pretty horribly in any situation where it would have to move. Since we have to farm 2 zones, 2 mini dungeons and belial cant be frozen, WD sustained DPS is a little troublesome.
3. Unless we have someone with a plvl 100 WD alt lying around we're going to be losing a lot of paragon levels worth of DPS stats. That 300 str from a plvl 100 barb is gonna make the DPS output of our barbs closer to that of WDs.
How it would work in the specific challenges:
Ubers + 2 mini dungeons:
Party would wait in town while the monk uses DS to get around to the 2 dungeons. As soon as he engages the first pack the CM + Barbs jump in and destroy everything in that dungeon. Since it's a full clear of the dungeon afterwards they port back to town as the monk DSes towards the next dungeon. Barbs leave the game to reset WotB CD. Repeat for the next mini dungeon.
For ubers, CM needs to get a perfect freeze so that barbs can get double hammer to maintain BR bonus. For SB Kulle, the monk should be positioned the closest to SB so that when he initiates a grab, the monk gets picked up. While in the air the monk can still provide overawe, the EPs can still go off and he can still serenity the EP if needed. The SK Mag fight they should engage maghda to proc SK to TP.
Just waltz through the citidel with the monk CSing the mobs and the barbs rending/hotaing them down. On the purple mob, CM freezes, monk CSes and Eps the fallen master like mobs to help take down the single target faster. Barbs get a rend off and position themselves to hota the purple and EPed mobs. On the blue deceiver pack a CS will allow the 2 barbs to hota down 2 of the 3 mobs. EPs on those 2 should kill the last mob. If the barbs have lost wrath for some reason they can leave the game to reset it for belial.
Belial phase 1 and 2 are pretty simple. Phase 3 it would just require dodging the big explosions. I personally don't think trying to get ridiculous EHP to tank the explosions is worth it. Barbs should have enough EHP to survive the fist attacks though. Running bloodthirst for 8%+ lifesteal would probably result in them being able to leech back a majority of their life between the attacks so they can just facetank that portion of the fight. During the explosions they can stand still and HotA. The first explosion to hit them the monk can serenity it, but then after they have to be more careful. Monk and wizard just need to get try to get their party buffs off. I'm not sure if the freeze debuff will work on belial, but it still helps in the citidel so it should remain.
Core of arreat should be run just like in the citadel. If the barbs have lost wrath for some reason they can leave the game to reset it right before Azmo. Azmo itself will be a pretty simple encounter. Just focus on him and DPS him down....
Pretty much the same thing as Azmo. The only difference is that in phase 2, the barbs need to help CC lock shadow diablo so that he doesn't summon the clones.