So, I decided see if in 5.4 even with the new buff to wearing two PvP trinkets would make it better than using a PvE trinket, if you don't want to read stats the short version is that a PVE trinket will completely destroy and both the on-use and proc trinket!
Here's some math to help:
My Tyrannical On-Use agility trinket gives me almost 3k agility, which makes my weapon damage go from 12k to 13k a tiny bit more than 1k more damage on my weapons.
The Grievous On-Use agility trinket gives 3,670, more than half way to 4k agility, if we were to say that 1k agility gives 300 more weapon damage which I just tested by taking off my boots that give me 1,020 agility, which I know is more due to the 35% from leather spec and choosing sub.
So than 3670 would bring my weapon damage from 12k to around 13.6k or so.
5.4 Raid - Normal - Siege of Orgrimmar - Boss X Loot X - Agi DPS Trinket (4) Has 21,380 agility, even if it was nerfed to half like they have done in the past and doubled the duration that would be around 10,600 agility, resulting in a boost in damage from 12k to 15k. That's HUGE in PvP when my ambush does 470% weapon damage plus 3k. That would result with an initial ambush of 73,500 with the trinket proc, that's BEFORE find weakness! If I used the Grievous Trinket I would get 64,100. And this is before mastery vs. PVP power.
Now onto the mastery vs. PVP power! The PvP trinket right now has 2k PvP power. That results in 4.83% more PvP power. Now if I were to take the PVE trinket I would get 2k Mastery, which is 3.27 points of mastery. Right now I have 8k Mastery, which is 64% on my finishers, with 40% of that coming from my gear and not the baseline mastery. So if 8k=40% 2k=10% more mastery, which would put me at 74% mastery!
Right now with 54% mastery after taking off almost 2k mastery brings me to 54% making my eviscerate hit for 47,650. With that 10% more it goes to 60,150. That seems like a lot more damage than 4.83% even though it is just on finishers.
So in a highly unrealistic situation, where the trinket is NOT nerfed in PvP this is how hard my ambush would hit for, with the proc up, rupture up, shadow blades, prey on the weak 10% more damage mastery of subtlety, and find weakness, taking into account the 50% version, Resil WILL be calculated after. Note this is on a warrior that has 50k armor, bringing it down to 25k which would be a 26% damage reduction.
Ambush no Resil all CD's:
The proc gives about 6300 weapon damage, giving me 18400 weapon damage.
89,480 ambush damage with just the proc up
10% of that is 8,948 so with Mastery of Subtlety and Prey on the Weak that would bring it to 107,376
Having Rupture up would than add 17,896, coming from the original damage of 89480. Adding up to 125,272 Damage! Now for PvP power, which at the moment with no PvP DPS trinket and straight up full Tyrannical gear I have 30% PvP power. Bringing that to 162,853!
Now for the reductions. First armor: 120,511 than with 65% Resil: 42,179 NON crit! That's more than I'm doing on an lvl 90 target dummy with a 41k Ambush with Rupture, Find Weakness, and Mastery of Subtlety up!
For eviscerate with just the proc up would hit for 143,000 before Resil and armor and all the buffs up.
Now all of these calculations were done wearing full Tyrannical, which means that the damage would be even higher with 5.4 hits and the new gear comes out!
Also I would like to note that this is also self-buffed, meaning I don't have any mastery buff, crit buff, kings or might. And is also taken into mind that your first attack would be Garrote to set up the buff and Find Weakness and have the SV buff up, than to Ambush right after so that you have the full 21k agility on your Ambush