The first Warlock will always be doing Elements, it's by far the biggest DPS gain for 9 out of 10 raids. (You have to be stupidly heavily melee stacked and/or against gimmick bosses like Vael for CoR to be better).

If your goal is two warlocks, then you either have very few of them in your guild or have them sit around a lot. Assuming you can't get away with the second, it's entirly possible to have no warlocks show up if you only have three of them in the guild.

I'm curious where the number of 20 to 26 effective resist for a level 63 mob comes from. I've been picking up the spell pen pieces that were going to rot in my guild and testing them, and I feel like it's significantly improving my overall dps. My Average shadowbolt went from 1900 to 2300 on patchwerk with the addition of 40 spell penetration. Right now I'm sitting at 60 spell pen, and I definitely hit higher avg shadowbolts as compared to the other 3 locks, by 300 to 400 damage, and a couple of them actually have more spellpower and % hit than me. It may be luck or some other thing I'm not seeing, but I'd attributed it to my new gear.

Another thing I noticed was people saying that Glock will always think a mob has about 20 more resistance than your total spell pen. It's been my experience that the mod thinks the mob has exactly as much resist as you have spell pen, and doesn't add a flat 20 on top. The cool thing about the mod is the sync tool though... when I started syncing with 2 other locks in the guild, even though with CoS and 60 spell pen, I was showing some mobs as having only 100 shadow resist, and I noticed I didn't see any more partial resists on them. I checked with the other 2 locks, and they had recorded a few partial resists while I had none.

I do believe that Anub'rekan definitely has 140 SR... I went from having 40 spell pen to 60, and his resist number stayed locked in place, it didn't go up by another 20. If I can get the next robe off C'thun, I should be over 140 total penetration, and I can really see if it throws the numbers off.

Meh

Why cant there just be one unanimous answer to this question.

From what I've read I have worked under the assumption that spell penetration did nothing PVE. However if thats not the case (based on lasiders analysis above) then itemisation is seriously messed up. eg Doomcaller Chest becomes vastly superior to Plagueheart. Surely that cant be right :s

http://forums.elitistjerks.com/viewtopic.php?id=6450

Penetration gear is useless on mobs with less than 75 resistance to your element assuming the appropriate curse is kept up. As said above, the hidden 5% partial resists on bosses are usually the reason why it looks like (from combatlog or parsing mods like GLOCK) you don't have enough resistance reduction.

Thanks for the link, those are some very interesting tests. I'll try to get more concrete data and figure out if I really did see a reduction in the amount of partial resists I was getting, or if it was a placebo effect.