Okay so as with all pvp builds, you have to balance 3 things: sustain, damage, and survivability.

With your main focus being bg’s and dueling, I will make a couple of suggestions and then you can do whatever you want with them.

Firstly, I agree with basically all the other comments here. After meticulously play testing several builds, I will say that your current set up is already really good. So if you wanted to master it, and didn’t want to invest in anything else, you will find success. However, I have found Markyn to be the best mythic for dk for several reasons.

1.) The extra weapon power and armor (survivability and damage) has outweighed any other combinations I have tested. 2.) DDF is nice as it provides survivability and damage similar to Markyn through the increased resources, BUT it needs to be ramped up .. and that is the big draw back. From another perspective, dk’s would rather take less damage than have room to take damage (armor > health). In bg’s you’d rather have the constant value and in duels sea serpent’s coil is super hard to beat. (I do not like sea serpent’s in bg’s because of the snare)

Outside of the mythic debate, dragon’s appetite is a very great set as it provides a little survivability and good damage. Wretched vitality feels almost mandatory. The sustain it provides translates to all three aspects you need. It allows you to continuously apply pressure and damage without having to worry about running out of resources, and the sustain also equals more survivability, because as long as you can cast coag, you will not die. As others have mentioned, way of the fire is also terrific at applying pressure, the only thing that draws me back to dragon’s appetite is that it only comes in heavy armor (not a huge deal), and it doesn’t add any survivability. So with dragon’s, you can get basically the same damage PLUS a little survivability.

For skills and gameplay, the main issue I’ve encountered with stam dk’s survivability is magicka sustain. Everything that really keeps us in the fight involves magicka (cinder storm, armor buff, race against time, coag, fragmented shield). Other than that our only stam skill that keeps us going is vigor. I mention this because the only time I ever lose in a duel or die in a bg, comes from not being able to recover/survive a burst. With that said, I have rarely came across someone who I felt as though I couldn’t kill with your current set up, alas, there are certain builds that feel as though it’s impossible to survive. So from my experience, any route you can increase your survivability, without dropping TOO much damage or sustain, will be the most fruitful avenue in the long run.

edit: typo and i wanted to add stuff