Norngahl:
@Zorn
Hi!
Thanks for your quick sum up, but I have to speak up against some of your conclusions.
1. Bull Centaures
I use them as 2x4 BC with Full Command, Great Weapons, Shields and Gleaming Pennant. Comes down to 470 points but heck, they are worth it.
They get 13 S6 attacks in CC + 4 for the stomps. If you think about the point costs, you may feel that 2 attacks are to low and that they should be at least 3 attacks each.
BUT you seem to overlook their defensive stats… T5, 3W and 2+/3+ AS vs. shooting/CC makes them pretty hard to crack up, especially against targets with S5 and lower. While they don´t have an overwhelming mass of damage output, they keep their decent damage output over several rounds of prolonged combat, as they are pretty tough to kill. Do not forget with mobile S6 they close the gap in the CD army. You can easily shove them down the enemies throat, charge them into the hardest hitting enemy unit and expect them to do well. Sure, with few high S attacks they are meant to be Elite killers… If you send them into slaves, you´re doing something wrong. But last game when I saw them eating 2x14 Chaos Warrios, 20 Chosen (without 3++ blessing, granted) and a wharshrine I realised, they are a pretty decent anti-elite unit which is meant to do the jobs you shouldn´t send your other troops into.
Sure, a Kdaii Destroyer is impressive as well. But do remember, that with monsterous cavalry they deny stomp attacks as such AND they are more survivable to cannons AND they also grand your big ones a “pseudo” wardsave like the italians did with their bloodthirster/bloodchrusher combo.
Actually, I really like the bull centaures. I don´t say they are better than the Kdaii Destroyer, but they´re also not worse in my opinion. They simply play a bit different.
Use them upgraded as 8 man squads as a hammer and shove it into the most expensive unit you can find (works even better if you softened up the target with your warmachines) and watch them work.
2. The Kdaii Destroyer
It´s a great unit, granted. Nothing to say more. Great bang for your bucks. I guess everything was said before, great unit. The only thing I don´t like about them is that they´re being unstable… One bad round of dice rolling on your side and a decent passive boni + 1 or two lucky wounds on the opposite can seriously ruin your day. He is still vulnerable to units with many attacks and/or poison, as the 4++ doesn´t prevent you from this pretty good… I wouldn´t charge him into which elves, which are is anti- unit… 30 of them ranked up with 3 attacks each and poison might be pretty bad for him. Nontheless, great damage output and good defensive qualities. Unfortunately, you will hardly ever field two of them as they are rare 
3. Infernal Guard
As already stated in other threats, with the price increase Fireglaives and Blunderbusses are out of cost/effectiviness relation for me. So with HW/S you should build around their defensive nature, using them as the bunker for your chars and to soak up small-medium targets. Guess something around 25 bodies should be right for them, depending on what opponent you face you can field them 5x5 or 3x7+4.
They are fair for what they cost with HW/S. S4, T4 and 3+/6++ are a very good base for 12 points and a CORE unit and they are tough victory points to get. Sure, you can field 40 of them as well with success, but I rather prefer some more tactical flexibility and take some different units along their side, for example
4. Hobgoblins
Which are pretty decent with 40 bodies, HW/S, Banner and Musician as a tarpit unit and a passive combat resolution bringer.
Either use them to tarpit whatever you don´t want to face for at least two turns, more often 3 turns, or you use them to join an already existing combat to make use of the backstabbers rule… Just think of +3 from ranks, +1 from banner, +1 from charge, +2 from rear charge, +1 from backstabbers… +8 is pretty impressive if you ask me
Either way, they are good combat units, and even with 4 points each, they fill another gap in the CDs army- bodies. Heck, I´d even take them if they were 5 points… We´re not nightgoblins with LD5, our generals easily have LD10… So let them be somehow more expensive, I don´t care. They do a great job.
Bows are a nice thought, good in very shooty lists. Otherwise I´d rather concentrate about their defensive role, to deny kills to the enemy, remain steadfest as long as possible and make biggest use of their passive boni.
5. The Iron Dameon
I don´t get it how someone can say he´s bad… I think the cannons are just great! Usually 4 hits with S6 armour piercing and D3 wounds per hit seriously kill all enemy monsterous cavalry, lone characters, warmachines or monsters… Get rid of hydras, steamtanks, bloodchrushers from the far distance. That´s something a magma cannon cannot do. Sure these are S5 and flaming doing d3 wounds, but they only ever inflict one hit per model underneath the template so they won´t ever cause more than 3 wounds on a single model per turn, so the daemons cannons are still better to get few or single models of the table in only one turn, especially because the cannons are S6 AP.
I really love this unit, esepcially just for it´s cannons. CDs lack movement, so you have to be shooty to equal this. A fast and sneaky enemy will circle you, making your slow and few CDs always running behind him, just reacting than acting. Once he got your warmachines, your phase is over, as then he´ll get you with his movement in combined charges and so on.
Really, beside IG with fireglaives, the daemon is our only truly reliable shooting using it´s BS rather than throwing artillery dice. The smaller the targets or the harder, the worse our warmachines are. The daemons cannons fill this gap, as he can put several hard hits on a small and/or hard target.
Really, I love the Daemon to get tough units off the board as fast as possible. Granted, the magma cannon does of course better against bodies.
Therefore you should take a magma cannon AND a Daemon to get most out of your stuff 
But don´t think the daemon is better… He´s a great tough-several-wounds-model killer, the best CDs have.
In CC he causes 2+D6 S7 impact hits which hit automatically… Fair 5 hits, 4 dead models… Great against elite as well. With unbreakable, 3+ AS, S7/T7 and 7 wounds he will hold up nearly everything in the game for the whole game. I consider this a nice addition to use when the cannons did their job they were meant for. Use him to join existing combats or smaller/elite units and you´ll see he´ll work gread.
Enemies body units should be the target of our deathshriekers/magma cannons and our IG with HW/S to eat up the rests… They will do great in this role, hitting on 3s, wounding on 3s, taking as good as no wounds in return
Conclusions:
- Use your Warmachines against bodies, starting with the most efficient enemy (knights for magma, big blocks for deathshriekers 5") and so on.
- Use your big ones (Iron Daemon, Bull Centaures, Kdaii) against the hardest enemies targets on the battlefield, starting with the ones that threat you most (usually monsters/knights/chosen/monsterous cavalry and fast units that get close to your WM)
- Use your core to kill easy-medium units that already had been bothered by ur warmachines and they will excel at their task. That´s what they were meant for, to soak up the rests.
- Hobgoblins as passive CR generator or steadfest block, or, if you face much mass units/MSU, use them as a horde to get 30 attacks. Remember, LD10 (SP, DS with banner of discipline) general baby 
That´s just my few cents. Will post somthing about the other units tomorrow.
@Thommy
Fixed
@Borin
Okay, understood. Non the less Hobs are cheap passive CR and sacrificial units CDs lack.
They’re sturdy.