[Prince of Terror] How does it work?

Hi guys, I finally managed to obtain this perk and I was running around yesterday with it in minigame to test it.
First of all a little description of what it does:
Prince of Terror:
+89 Magic Damage (Fire)
+375 Protection (Fire)
+66% Weapon Damage (Fire)
Duration: 15 Seconds
Casting Time: Instant
Cooldown: 60 seconds
Chance on Damage, Spiritual Wrack (-10% Holy and Unholy damage) 200 proc per minute
Switches the damage type of the combo from fire to Unholy and improves the BtD combo with an increased chance of critical damage for the DoT.

This is the description of the skill itself I would like (try at least) to go a bit more in detail about what a HoX may lose/gain from removing RSoX to use PoT.
This is very depending on the setup of perks and equip you have so I will give you my example so you can do your calculations on a solid numerical basis.
I'm running around with a most classical Possession/General, 56/23, using in PvP Chest, Legs and Helm from T1 PvP set, boots and belt from PvP minigame set, 2x Dreamer's Keepsake, pvp5 Cloak, pvp5 necklace, pvp5 sword, t2 wrist and t3 shoulders and gloves, PvP level 5 with T3 BK.
My original setup was: Chromatic Warding (3), Decisive Strike (4), Will of the Sublime (4), Ethereal Escape (4), Red Shadow of Xotli.
My stats: 340 strenght and 230 Intelligence without RSoX and 440 strenght and 330 Intelligence with the passive boost of RSoX.
Resistances; passive resistances from AA at 2, beside Electrical which is at 3.
With this set up my PvP magic damage was at 1055 Bonus spell damage fire, with resistances between a minimum value of 28% up to a max value of 31.5%.

It's quite clear that removing RSoX it's putting our magic damage down to Oblivion, in fact as soon as i removed RSoX I notice my pvp magic damage fell under 1000.
It's obvious that this gap will be increased while under Desecrating Essence, given that without RSoX we will lose our massive stat increase.

Now my actual setup with PoT:
Build: it's the same Poss/Gen I actually don't find doable a switch to an Avatar/Poss or Poss/Avatar, General tree still gives us more than Avatar does.
Perk setup: Field of War (pvp perk at 2 points, being trained at 3), Decisive Strike (4), Will of the Sublime (4), Ethereal Escape (4), Prince of Terror
Equip: the very same described before.
Stats: Strenght 340, Intelligence 230, PvP Bonus spell damage 1033, Resistances between a lowest value of 26.7% up to a highest value of 28%.

Little overview: I'm standing above 25% of magical resistances, admittedly the difference between 26% and 28% it's probably not that much, the magic damage it's only 22 points below the average I had in a normal form with RSoX so it's highly acceptable from my point of view (soon i'll have field of war at rank 3 so i will go on pair probably), yes of course while in form the gap will be present but on the overall this setup from my point of view fills the gap existing due to the absence of RSoX, and more than this, honestly a possession HoX does not rely that much on remaining under Desecrating Essence for a long time, that's more an Avatar feature.

Test during fights:
Ok then, now let's come to the real test.
Prince of Terror being an instant cast spell it's extremely dynamic, it can be used whenever you want, immediately giving you a good burst of damage.
I'm actually not suffering from the absence of RSoX, and the damage output it's pretty much the same, what is nice is that Pillar of Infernal Flames has a huge benefit from this perk, boost to magic damage, boost to melee damage, auto-debuffing, switch to unholy damage, it works great.
We should also consider that PoT and Exultation of Xotli can be applied together, this will then result in a nice situation:
90% + 66% = 146% melee damage istantly for a lenght of some seconds resulting in a good burst of damage, let's just consider that my melee dps goes up from 209 to 290 only with the +66% of melee boost!
For example, yesterday I managed to land a BtD for 800 melee damage for each hit plus a boosted dot at 700 on a soldier.

Conclusion:
Prince of Terror has impressed me, it's a perk that can be used in many situation and grants you a good boost, used properly and cycled with other skills like Demon Maw, Tome of Erlik, Desecrating Essence will allow you to have a boosted damage pretty much for the whole duration of the fight.
Anyhow the differences between PoT and RSoX are really not so deep to allow me to say that one is better than another, I'm strongly convinced that is more a matter of personal tastes and gameplay.

So even if I do believe I will hang on with PoT for a while, my suggestion for you is: Try it out, make tests, make experiments!
Hopefully my numbers posted above will help you a bit to understand what are we talking about

Catch you around!

Arcalimon

[Note: Thanks to Kayava, Igramul and Kelvar who helped me about this topic]