Yeah, I’m not too sure why I was getting stomped at the end, either. lol. I had figured from all else I was experiencing that it would be rough but doable. From what I recall I did well during about the first half but once he started summoning minions in things started plinking me quickly. And I think there was some other attack he had, don’t know which one, that would hit me hard and fast. Its so difficult to track what’s eating away at you. 
The helm is a left over. Back in that level range I had all pieces of Perdition and was using them until I found better pieces to swap them out with. I had hoped over to FG as per your suggestion so had picked up the lower helms there earlier but only went back, later on, to hunt for the Gannar’ Sting.
One thing I was doing while deciding on swapping was watching how it affected my DPS. I’d swap it in, check the DPS results, and if it didn’t give a major increase or didn’t offer other benefits, then I’d hang on to what I had. – not the best way to go but I was focusing on killing them quickly with the DoT effects.
As for the Corpse Dust, at the time I had plunked that and Soul Shard into the rings, I was trying to boost my Vitality Resistance up to 80 as it felt like I was getting a lot of bleed and other Health draining effects. And, one of my many bad habits is not looking back at my stuff to see if I need it in place any longer (which, now checking, I don’t seem to need). So for the Mark of Illusions, am I taking it for it’s Defense and ER or for it’s Elemental Damage? OR both? 'cause I usually skip ED as it doesn’t sound like it would boost A&P Damage.
The AvS in the helm is leftover so mostly just an act of sloppiness. The shoulderpads I picked up towards the end of Malmouth. I was really rocketing up in levels at that point and I first looking for something to make up for my chaos and aether R and after searching a lot I just kind of gave up and said I’d get back to that later. Same for the belt. I got it, searched some, got tired (I do most of my playing after work, late at night) and figured I’d get back to it.
I think, over all, I’m more looking at what new item I can equip a component too rather than looking backwards. Taking a look at Sanctified Bone, I’m like… yeah, that would’ve helped a lot for my resistances. I’ll make sure to slap one into my next helm.
As for stopping, mostly I’m just kind of getting burned out on GD. I’ve got 12 characters I’m bouncing around with. I maxed one a couple months back on this build guide (and I’m sure the build is way out of date) but the rest are in the low 30 range. And there’s a lot of repetition of builds as I experimented or followed builds (I still have your Nephrite Spell Binder build to follow through on.)
Right now I’m searching for a good pair of lvl 70 stingers (and maybe look for that Eye helm, too), then see how I feel about diving back in to progress along more. I will take a look at your component guide as you’ve drawn it to my attention. You usually lay stuff out pretty well so I like your guides and stuff.
I guess while I’m here, in the build guide, there’s either mention of putting a point into Resilience as you’ll link Giants Blood to it later on, but you’ve dropped Behemoth from the build I think so do you feel that the point in Resilience is still warranted?