Well, you didn't say your spec, but for both specs the 4pc is a good bonus so you're going to want the 4pc bonus. The BiS setup involves shoulder offpiece, so you're going to want to be prepared to use the helm as tier at some point, but your specific situation I'd use boneplate helmet and on the offchance everyone else gets their shoulder pieces before you get the offpiece shoulders go ahead and swap the helms to maintain your 4pc with offpiece helm.

You aren't replacing heroic versions, so yes swap to the RF versions as they are significant upgrades.

Simulationcraft Results

pretty much covers it as far as proof goes.

As for tanks getting it over Frost DKs, that's up to your guild though it can be argued that due to most fights having a strong DPS requirement that the weapon is of a greater need for the DK as the DPS increase is smaller for tanks (the proc is stronger, yes, but they scale less from WDPS). Additionally, Souldrinker is less predictable than the pure mastery and dodge from Mandible so the tanks should stick to that as the higher WDPS isn't needed for TPS.

Necroing this a bit just to address a couple things.
First, I'm unsure about your AMS use. Are you using it to stay in for hour of twilight? If so, have you found a way to reliably survive HoT? Because first of all, I've found it too rng to stay up on normal (much less heroic). Even with AMS/AMZ/IBF, I've found an unlucky pulse on either shield before HoT means I'm dead, so I'm not usually a soaker.
On the other hand, I'm an emergency soaker so I save all my defensive cd's just in case I'm needed to take a HoT. This means I don't get the luxury of using AMS offensively except in LFR. Great for you if you do.

At any rate, if you're using AMS to soak pulses, then you're still going to be getting a lot of RP from each use (and more so if you manage to soak an HoT with it). Basically, I'd say you will get RP capped no matter what. The best thing to do is to only use it when you're resource starved (since pulses happen often but typically aren't really a survival threat); then you can go to town with the free RP. Otherwise, your last sentence of weaving rune strikes with DCs is a nice succinct description of your default approach. Don't get too upset when you do cap, however. In that case, don't let too many Scourge Strikes sit on the table (they're still #1 imo), but do fire off as many DCs as quickly as you can.

Would a Masterfrost rotation benefit more from a Glyph of Icy Touch than Glyph of Obliterate?

What's a good mark to shoot for in regards to Dark Transformation uptime? 60/70/80%?

If you use Blood Tap as an unholy DK and are left with an unpaired frost rune should you use it on icy touch or just let it be? I find my diseases sometimes drop off because it messes up Festering Strike usage.

If you have an open global with <34 RP and no other runes to use I can't see why you shouldn't use it.

There is no haste cap - not even a real softcap.

If you're using the normal priority, get as much haste as you can to where you feel you aren't wasting resources, after that point, get mastery.

I guess the better question then would be: what "comfortable" amount of haste are most of you DKs shooting for, while following the normal rotation, before reforging to mastery?

Without t13 2p you can go pretty high (higher than you can actually achieve with available gear in most cases), but with the 2p somewhere around 1900 is where you probably want to be, give or take.

Hi All

As im a lower geared player all i can really compare myself to is simulationcraft. At the moment, with skill level set to average i am still around 2.5k dps behind that of the sim when against a dummy (i pull around 18.5k and sim says u should be around 21k). how close should i aim to be to the sc result?

Thanks in advance!