I just tonight completed the 4pc and tried it out for the first time this tier, and it seemed like my fingers were going to fall off, and the damage was okay but not near what I saw as assassination pre 4pc. I'd be interested if you discovered any tricks along the way for certain fights to improve edps. Thank you.
What you definitely need, although you should already have it before getting your 4piece, is some sort of anticipation charge tracking. If you're interested in a simple weak aura string, just PM me. Basically you'll do the same you did before getting the 4piece when AR+SB is used: Keep RvS/SnD up, SS up until you got 3+ charges, and finish when you got 3+ charges. Once you finished with 3 Anticipation Charges, it basically comes down to: finisher+2ss when you have 3+ charges, finisher+3ss when you sit at 2 or less charges. Since you will build 4 CP with 2 SS you should count on losing 1 CP, or 1 charge, with every set of finisher+2 SS.
It is also somewhat important with how many CP you finish your AR, since you will most likely sit at 100 energy and don't want to waste another second or two energycapped right after it. Going into AR with a maximum of 2 CP works best for me, that way you get exactly the right amount of styles+finishers into a single AR+SB to come out of it with 4 or 5 anticipation charges with your last 0.5sec GCD and then have 3 to 5 SS right after to rebuild your anticipation charges, KS, and finish twice to reduce your cooldowns by 20sec already. Also remember that while all your abilities benefit from the gcd reduction of the 4piece, the AR glyph only works on a selection of spells. So if you're responsible for keeping weakened armor up for example, do it before using AR+SB.
As far as "tricks" go, you will want to use your cooldowns the moment they come off CD, but deplete your energy beforehand. As long as you have a certain control over temporary buffs such as trinketprocs, another rogues tricks or bloodlust/racials, you should stack them whenever possible. Delaying the usage of KS or AR in my opinion is not worth the effort, since you will most likely lose out on one AR and/or KS. With a near 100% uptime, you can expect to have 1 AR every ~60-70 seconds and delaying KS for a higher Bandits Guile stack is only worth it when you only have 1 or 2 styles remaining to get there.
Regarding the current content, remember that maximizing overall DPS and doing the "right" DPS to beat the encounter are two different objectives. Since you will basically have AR come off cooldown every minute, you can use this knowledge to have it ready for important adds (the 3 big ones @ horridon) or important phases that you will want to cut as short as possible (iron qon p2). AR is one of the strongest cooldowns out there, not because of the raw dps it provides, but because it is available so often and you having absolute control over when that happens.
Does anyone know the value Mark for Death vs anticipation? Seems like MFD could potentially be a decent choice for combat especially in a long fight.
Playing combat without anticipation, especially with the t15 4piece, is something I wouldn't even suggest to my mortal enemy. While anticipation doesn't provide an active dps increase, and MfD does, anticipation makes your life so much simpler and will oftentimes safe you from overcapping CP or energy. The dps you gain by preventing that from happening is definitely worth more, than the 5CP every 60 second MfD provides.