Blizzard recently announced the Tier 13 set bonuses, and the Death Knight DPS ones are...interesting.

2pc - Sudden Doom has a 30% chance and Rime has a 60% chance to grant 2 charges when triggered instead of 1.
4pc - Runic Empowerment has a 25% chance and Runic Corruption has a 40% chance to also grant 710 mastery rating for 12 sec when activated.

Now, first things first - without doing any fancy math or analyzing how good these bonuses are, they sound pretty cool. Everyone loves getting free Howling Blasts or Death Coils, so getting DOUBLE free procs is even nicer! (There might be some GCD cap issues, but that's more complicated than I want to delve into in this post.) And a flat-out bonus Mastery proc? Well, it's not Haste (our best stat), but it's not bad, especially considering it doesn't involve us doing anything strange - no building stacks of something and then unleashing it, no weird situational benefits, just a straight up occasional bonus from doing our normal rotation.

HOWEVER, these bonuses are procs. And they proc...off abilities that are ALSO procs. (YO DAWG I HEARD YOU LIKE PROCS SO blah blah blah shut up.) Anyway, I'm no statistician or theorycrafter, but here's how I see the 2pc and 4pc bonuses when you consider both the Tier 13 proc rates and the actual innate Rime/Sudden Doom and Runic Empowerment/Runic Corruption proc rates.

2P Frost: Your Obliterate has a 45% chance to cause your next Howling Blast or Icy Touch to consume no runes, which has a further 60% chance to receive 2 charges instead of 1.
45% x 60% = 27% chance on Obliterate to get 2 Rime charges

2P Unholy: Your main-hand auto attacks have a chance (I did some quick tests and averaged 27% from some logs) to make your next Death Coil cost no Runic Power, which has a further 30% chance to receive 2 charges instead of 1.
27% x 30% = 8.1% chance on auto attack to get 2 Sudden Doom charges

Now...I realize the 2pc bonuses have slightly different triggers (an active spell versus auto attacks) but that proc rate seems quite off. I compared two top-10 World of Logs entries for a Frost and Unholy DK, on a Baleroc fight of equal length, and got the following results:
Frost DK: 59 Obliterates (27% proc rate would mean 16 double Rime procs)
Unholy DK: 90 auto attacks (8.1% proc rate would mean 7 double Sudden Doom procs)

To make matters worse, Frost's Howling Blasts hit much harder than Unholy's Death Coils. In those sample logs I've compared, the Frost DK's Howling Blasts hit for 21k on average, while the Unholy DK's Death Coils hit for 13k on average. Now granted, Unholy DKs do also get an extra benefit in that their Death Coils buff their Ghouls, but that's harder to quantify, and I'm not sure if it would make up for twice the number of procs on an ability that hits twice as hard. (I don't play Unholy, though, so I could be completely wrong on this.)

As a Frost DK, I'm not complaining about these results, but they do seem pretty weird.

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4pc Frost - When you use your Frost Strike ability, you have a 45% chance to activate a random fully depleted rune, which has a further 25% chance to grant 710 Mastery for 12 seconds.
45% x 25% = 11.25% chance on Frost Strike to proc the Mastery bonus

4pc Unholy - When you use your Death Coil ability, you have a 45% chance to increase your rune regeneration rate by 100% for 3 sec, which has a further 40% chance to grant 710 Mastery for 12 seconds.
45% x 40% = 18% chance on Death Coil to proc the Mastery bonus

Frost DK: 70 Frost Strikes (11.25% proc rate would mean 8 Mastery procs)
Unholy DK: 95 Death Coils (18% proc rate would mean 17 Mastery procs)

And here we have a reversal of the pattern, this time favoring Unholy. Maybe this is supposed to balance things out with the skewed 2pc bonuses?

Something else interesting is that for Unholy DKs, both their 2pc and 4pc bonuses directly affect their highest source of damage, Death Coil. Meanwhile, Frost's 2pc bonus procs off Obliterate, a primary ability that is typically *not* their highest source of damage (it's usually Frost Strike) and gives free Howling Blasts, another primary ability that ends up low on the overall damage chart. Furthermore, Obliterate doesn't benefit at all from the +Mastery proc.

In other words, Unholy gets a straightforward synergy with autoattacks proccing extra Death Coils and Death Coils proccing faster rune regeneration and a +Mastery bonus that helps Death Coils. It's wonderfully simple and circular.

Frost is a little more complicated, with Obliterate proccing free Howling Blasts, with the extra Runic Power gained from those Howling Blasts allowing for more Frost Strikes, which proc instant rune recharges (ie, more Obliterates) and a +Mastery bonus that helps Howling Blasts and Frost Strikes.

I have no idea how this will affect the bonus balance overall, I just found it interesting.

So Frost and Unholy DKs, get your Power Auras ready because it looks like 4.3 will be full of monitoring procs and RNG juggling. Of course, these bonuses and proc rates are only in the PTR phase and may all change completely by the time 4.3 goes live.

That being said, who cares about bonuses when WE STILL HAVEN'T SEEN WHAT OUR ARMOR WILL LOOK LIKE! Poor Death Knights, the only class to yet see our Tier 13. :(

/frosty, unholy, diseasey single tear