The guide is currently under maintenance. I'm halfway through the 1st post, and I haven't started the other two. I'm taking my time with this, so no ETA when I'll be done.
Recent changes to the Ulduar BiS list
Now, before I say anything, I'd like to clarify that I've already finished this section and written a thorough description. Here, I would simply like to expand on it. I don't want to do it in the guide because otherwise the section would become too long and complicated.
After revisiting my proposed BiS list, I was incentivised to experiment more with it. I read the analysis of the Ulduar items on wowhead, and I considered to give some strong standalone items (more specifically https://wotlk.cavernoftime.com/item=45461 and https://wotlk.cavernoftime.com/item=45611) another shot. According to the wowhead guide, those gear pieces weren't optimal because they had exceeded the Hit and Exp caps. However, now is the time to shed light on the biggest difference between Classic WotLK's version of Ulduar and the one in the original retail WotLK, which warmane is currently emulating. In warmane, Ulduar items retain their original, "retail WotLK" stats unlike Classic where the same gear had increased stats. Logically, the BiS build in wowhead reflected the environment there, but it cannot be applied to warmane.
Here, I'd like to open a parenthesis and say that I don't know with 100% certainty whether Ulduar will be released with the original, "retail WotLK" stats in Onyxia. I simply speculated based on my previous experience with Frostmourne (2020-2023), though I should mention that the warmane staff was willing to implement some
changes from TBC Classic in Onyxia. Still, I doubt they would release Ulduar with buffed stats because that would not only change the gear progression in Ulduar but also in ToC.
So, after revisiting the Ulduar section in the guide, I wanted to try out more builds and see whether I would find other gear combinations, and sure enough I did. I began comparing Horde builds feat. the Faceless cloak and Icy Intent:
(yes, I'm aware that the audio quality is Scheiße, but I'm not going to buy a new mic just for this video)
As you can see in the video above, both Rawr and the feral simcraft supported the usage of "Icy Intent" in the context of a Horde player. This is why the current BiS list promotes it. Now, before I move onto the Alliance build, I'd like to mention that the Faceless cloak surpasses Icy Intent when a player sockets 3xhttps://wotlk.cavernoftime.com/item=45987s:
Admittedly, the damage diff. is small, but the Faceless cloak outperforms Icy Intent due to the extra socket slot which is why I decided to include it in the guide. I'm going to talk about the Stormjewel gems a bit later, but as you can see being able to socket more of them leads to (slightly) higher numbers, and in this train of thought going for Icy Intent or Faceless as a Horde player depends on a person's budget.
I repeated the same experiment with an Alliance cat, but as expected the Hit rating from the Icy Intent Cloak collided with the one from https://wotlk.cavernoftime.com/item=45869 which resulted in wasted stats. Because of it, I considered using the wrist from Algalon and see how it would fare:
vs

It was inferior due to the wasted Exp stats, though I should mention that the same "Icy Intent + Solar bindings" Alliance build in full Agility showed higher numbers than the other one in full Arp:
vs

For Horde, the same tendency is also true but there are no changes to the items (arp build vs agility build).
Now, I want to tackle the topic of Agility vs Arp. In the original game, Arp first capped at 1232 and somewhere in ToC the cap was increased to 1400. So, during retail Ulduar the soft Arp cap was 567 with Mjolnir, and people still had room for delicate gems. Back when Frostmourne was running, it was based on the 3.3.5 patch for the most part (instances and content-specific items like the epic gems were released with the respective patch) which included the 1400 cap for Arp. As you can read in the ElitistJerks guide, post-nerf Arp outshines Agility by a bit when a person has around 400 with https://wotlk.cavernoftime.com/item=42995. With the proposed BiS list (and no gems), a person's Arp sits at around 408 which is exactly on the edge.
If we compare the pure Agility build with its Arp variant, we can see that Rawr favours the prior stat; it considers Arp to be below the desirable threshold. It only acknowledges the power of Arp in short fights, i.e. below 3 mins:
Now we need to take the length of the Ulduar boss encounters into consideration. In this youtube channel, most of the fights last around 5-6 mins. If we trust Rawr's assessment on the "Agility vs Arp" case, we should go with Agility as the majority of the boss encounters last longer than 3 mins. However, things become complicated when I take into consideration the feral simcraft. Even with lowered stats, it considers Agility to be inferior to Arp:
I want to mention that I've played around with Rawr, and I've edited the stats of the items there so that they could match their Classic counterparts. If every single item has modified stats, this program also shows higher numbers for Arp regardless of the fight duration:
However, I cannot do the same with the feral simcraft - while I can modify the passive stats on the bottom left part of the UI, I cannot change the proc effect of
Mjolnir. So, I decided to use Rawr again and keep all items except Mjolnir unchanged, but Rawr still favoured Agility:
Honestly, as I'm updating this post, I don't know which program to trust on this. In my opinion, going for either Agility or Arp is a matter of personal choice as 1) the damage diff. is very small and 2) both programs show diff. results.
After giving it an unhealthy amount of thought, I decided to change the gems in the BiS list section to Arp. While the damage diff. between both stats was relatively small according to Rawr, the feral simcraft heavily favoured Arp regardless of circumstances. Having said that, this doesn't take into account the fact that during Ulduar the Stormjewel gems were released without the "unique" tag which allowed some players to stack them. In the original game and apparently in Classic Wrath, people were restricted to using only one, but Frostmourne was an exception because, as stated above, it was based on the 3.3.5 patch while the Stormjewels became stackable in ToC. Now, I don't know if this will be the case when Onyxia releases, but stacking those epic gems is, objectively speaking, the best way to gem your character, as the extra stats are further increased by our talents (https://wotlk.cavernoftime.com/spell=33856 and https://wotlk.cavernoftime.com/spell=17051) + https://wotlk.cavernoftime.com/spell=25898 from paladins: