Keep in mind currently during DW encounter hit seems almost useless because you can't miss tentacles, claws, etc. (Not sure if you still need the 8%).

Has this been confirmed? Because the BiS list certainly didn't change anything.

The [Backbreaker Spaulders] should be the off set since they are upgradable to heroic unlike the [Bones of the Damned].

Is the OP at any point going to update his BiS list? As it is now using items that don't exist ingame and weapons that aren't BiS.
Keeping a non-correct version here is just going to cause confusion.

The Heroic Runescriven Demon Collar from Heroic Hagara is better than the demonbone waistguard from VP

I have the 397 version. Its damage is what's listed on wowhead(9063-13594) + 67.5%*AP. It is reduced by armor, which is bypassed with CS up, and benefits from physical damage mods both on your character and on target, e.g. DW/Enrage/Blood Frenzy all modify it. It's able to crit, which I assume is a chance equal to your melee crit chance, but I don't have nearly enough data to be sure, and it deals double damage on crit(probably 206% damage with a 3% crit dmg meta, like Fiery Attack procs, but again not enough data to say for sure). Crits do not proc DW, but they do proc flurry.

One oddity is that the ICD appears to be 27s rather than an even 25. After trying about 30 times to force a proc in under 27s(by simultaneously cleaving/WW multiple dummies to give it a high chance to proc if it were outside the ICD), I never saw lower than 27. If I had to speculate, I would guess the ICD changes between the various ilvl versions and the heroic version might have a normal 25s ICD. According to wowhead's data, the chance to proc outside the ICD is 15%, which is probably trustworthy.

In any case, from some napkin math, I would currently place the 397 version's proc's SEP value at roughly 395 in pure single target situations, which makes it a clear step up from H-VoA, and just a bit behind 403 Eye of Unmaking/397 Creche. If there's even a small amount of AoE on a fight, it is absurdly better than any other trinket option.

Is Gurthalak BiS for offhand too? Wouldn't the mace be BiS for OH considering the fact that procs are halved in the OH?

If you have the weapon please test this yourself, but I do have the weapon, and have tested this many times...

*****The weapons proc effect will happen from ANY type of direct physical hits you cause(melee, bt,rb,slam,hs,etc.) It does not matter if the weapon is in your offhand or mainhand, any of the hits you cause will proc it....
This also means that the offhand and mainhand will have the same chance of causing a proc.

I am going to guess that having 2 of the weapons will double the chance that you get a proc, and that all procs will still come from any of the direct physical hits you cause.

Well no. Only 1 of your abilities uses both weapons and so your cant get procs off the rest from the off hand. If you were to analyze just your auto attack then yes you would be correct, but with abilities added in you will get 1/3 to 1/2 more procs from your main hand than your off due.

Deep Wounds from procs have yet to be removed in the sheet, and proc damage is kind of new so the sheet might not be 100% correct in the regard of a BIS Gurtalak, especially in offhand.

Perfektion, do you mean that by equiping the weapon in OH it will proc from MH abilties like BT, slam and HS?
If so, could you share your tests with us? (for example, linking a proc from a BT while it's equiped in OH).