Help with headsplitter

what IO set do i pop in there

Yeah, the Armageddons are arguable. It depends on how you fight, and what you care about fighting. I figure I can munch through minions fast enough, and it's hard targets where I really want the DPS. And Broken Prey is right about the Fury of the Gladiator proc, and I wouldn't put an Achilles Heel in an AoE either. I should have the write up on that around here somewhere... ah, here we go. Oh, man, I made notes to myself about how I needed to revise it, so I have to rewrite it anyway. *bleah* Nah, I'm lazy. I'll just leave the revision notes in, and attach it as is.

Lets say you're surrounded by five even level minions and you use a PBAoE with an Achilles' Heel proc in it. With a 20% chance of firing, on average it will hit one of those minions. Achilles' Heel is basically a buff – attacks on that minion over the next ten seconds will do 20% more damage. So we can consider that additional damage to be the “damage” that the proc does. A level 50 minion has 430 hit points. Let's say that the attack with the proc did 190 hit points of damage, leaving the minion with 240 hit points. And lets say that you DO manage to kill the minion in the next ten seconds. The 240 hit points of damage required to kill the minion can be considered to be 200 base hit points of damage, plus 40 hit points of damage from the proc. So what's the MAXIMUM damage that the proc can do? It would be in an AoE that does NO damage itself, so that the minion still has all 430 hit points of damage. And then you'd need to finish off the minion in the next 10 seconds, which pretty much means finishing off the whole crowd in 10 seconds since I don't think there's a way to identify who got hit with the proc, or at least not to do it quickly. You would then attack the minion for exactly 359 points of damage, and the proc would do the other 359 * 20% = 71 points of damage.

So the proc does 71 damage to an even level minion under nearly IDEAL circumstances –your AoE does no damage at all, and you finish off the crowd in the next 10 seconds.

What about a regular damage proc? That's a lot simpler. 20% chance of doing 71.8 damage.

So when fighting minions, even under nearly ideal circumstances, the Achilles' Heel proc basically only pulls even with a regular old damage proc. In practice, it'll be way behind.

What about lieutenants? Well, you won't be surrounded by just five lieutenants and nothing else, and good luck finishing five lieutenants off in 10 seconds except with an AoE monster, but sure, let's say that everything comes together just perfectly. A level 50 lieutenant has 805 hit points. So you're doing 671 damage, and the proc does 671 * 20% = 134 damage to finish off the lieutenant. Then yes, under these even more ideal circumstances, the Achilles' Heel proc will do somewhat more damage than a regular old damage proc. But taking into account that not everyone's level 50, that you won't often find yourself in this situation, that your AoE actually does damage, and that sometimes you won't finish off the guy that got hit with the proc in the next 10 seconds, I wouldn't say that it's necessarily better in practice. I'd probably still recommend a regular damage proc as being more likely to do more damage on average, and to do it sooner since it takes effect on that attack rather than on potential future attacks. But even if we take the 20% chance of 134 damage at face value, what about a purple proc? That's a 33% chance of 107.1 damage = 35.343 damage on average, compared to our 20% * 134 = 26.8 damage on average. So the purple proc is still significantly better than Achilles' Heel against lieutenants even under near ideal circumstances.

So we pretty much need to get up to boss level before the Achilles' Heel starts to really beat out the alternatives. And while you might be using AoEs on a boss farm, you're not going to be finishing off that crowd of bosses in 10 seconds unless you're on a big AoE team. So I suppose I could add a qualifier of “unless you're AE boss farming on a big AoE team” to my advice to skip Achilles' Heel procs on AoEs, but that's seems unnecessary, that being such an exceptional circumstance.

So the basic use of Achilles' Heel procs is for taking down single hard targets. It's a single target because you don't usually find or take out multiple hard targets fast enough (with some exceptions on some teams). And its a hard target like a boss or above because only those have enough hit points for the damage from the Achilles' Heel to add up.

Now, I DO see some logic in putting it in AoEs for another situation – attacking the boss, but using an AoE because there are other enemies around. The primary target is the boss, so it's pretty much like putting it in a single target attack at that point, which is to say that it is worthwhile. However, what percentage of time do you use your AoEs that way specifically, and what percentage of time do you use them on targets other than bosses? Generally speaking, I think AoEs are largely used as minion munchers. As such, the Achilles' Heel procs are usually going to be outclassed by other options, often significantly outclassed.

REVISION: If the AoE has a regular damage proc, it is all but guaranteed to do full damage, because most AoEs don't do enough damage to kill the minions in that one hit, even when the proc hits. You could always be finishing off something with an AoE, I suppose, in which case a regular proc wouldn't hit for full damage. But if you're finishing off something with AoE, the Achilles' Heel DEFINITELY isn't helping, since it just sets you up for future damage. So we're talking about that initial hit. With an Achilles' Heel, some of the extra damage buff will almost always be wasted on blowthrough damage. In other words, you're not going to do exactly 359 damage, and the proc does the other 71. You're just as likely to have your last attack do blowthrough damage, in which case the proc also isn't contributing as much.,

REVISION: For the AoE attack on bosses, not particularly useful because your single target chain should have a bunch of Achilles' Heels, and stacking makes each additional one less useful. Depends on primary, of course.

Like others had said... depends on the build
I like 4 Erads and 2 Scirocco if its paired with a WP or Inv and 5 Arma for the others.