The other day I was running Heroic Pit of Saron with a dual wield Death Knight frost tank and Rimefang's Claw dropped. Said Death Knight began jumping up and down with great excitement. Now at this point, I should add that I'd spent a majority of the instance run feigning death or switching to viper to make sure that the mobs were paying the tank sufficient attention and not trying to claw my face off. You see, the dual wield Death Knight had threat issues. He/she seemed like a nice person, so I didn't really have the heart to burst his/her bubble by sharing what little I knew of dual wield tanking -- dual wielding two fast tanking weapons just isn't a great idea.

You see, six months or more ago, I toyed with the idea of switching to the Horde. A horrendous run of PvP failures, as well as minimal success PUG'ing raids, lead me to look for greener pastures. So off to the Horde I went. I rolled a Death Knight, purely to skip through the initial 55 levels that I didn't particularly feel like re-living at that point in time. I got to 80 soon enough and began gearing up as a frost tank. That's when I discovered the dual wield talents, Nerves of Cold Steel and Threat of Thassarian, and the fact that dual wielding two peace keeper blades would look bad ass. Tanking the 'entry' level heroic dungeons, things went relatively smoothly. Or so it seemed. But the thing was, the bad guys died so fast, any issues that I had in terms of my tanking went largely unnoticed. When the Ice Crown Citadel (ICC) 5 man dungeons were released, and the bad guys were a little harder to drop, a few issues started to reveal themselves. Number one being, I was having a hard time maintaining the attention of the bad guys I was supposed to be tanking. I told myself, "I just need to upgrade my gear, then I'll be fine again". But no. I started doing some research. My rotation was sound enough, as was my dual wield spec, so it had to be gear... and it was. Just not exactly what I had expected.

So after dual wielding two Rimefang's Claws without much improvement in maintaining threat, I started doing some research. Everything I found pointed to the same conclusion, dual wielding Death Knight equipping two fast tanking weapons will produce significantly less threat than a dual wielding Death Knight equipping two slow Damage Per Second (DPS) weapons. Initially this concept seems counter intuitive, I mean if you are tanking surely two tanking weapons are the way to go? Short answer. No. Unless an updated slow tanking weapon (a modern version of the old school Broken Promise perhaps?) appears in game, two slow DPS weapons are the way to go.

Let's have look, using my very basic math, at the different between dual wielding two Rimefang's Claw's and two Nighttime's - a slow DPS weapon of the same iLvl and also available from an ICC dungeon.

This analysis relies on the following assumptions:
(1) as a dual wield Death Knight you've had the good sense to spend three talent points in Nerves of Cold Steel.
(2) you've also spent three talent points in Threat of Thassarian.
(3) When each weapon hits, it hits for its theoretical maximum.

* If you are struggling for a dual wield tanking build, here's a basic cookie cutter starting build, with four points left over to do what you like with.

Based on the above assumptions, damage from the main hand weapon is 100%. The off hand carries the 50% damage reduction penalty, with Nerves of Cold Steel is applied after. Therefore, assuming three points have been placed in Nerves of Cold Steel, the offhand will hit for 62.5%.

Now lets look at the two weapons we'll use for the example:

[Rimefang's Claw]: 213-396 Weapon Damage, Speed 1.70, 179.1 damage per second.
[Nighttime]: 325-605 Damage, Speed 2.60, 178.8 damage per second.

It's important to remember that a large number of death knight abilities are based off weapon damage. Weapons with a slower speed usually hit for substantially more damage per hit.

First we'll use Obliterate as an example, assuming no diseases are up and no other modifiers are in play -- to make the math easier. Obliterate hits for 80% weapon damage + 467.2.

2 Rimefang's hitting with Obliterate.
Rimefang main hand = 316.8 + 467.2 = 784
Rimefang off hand = 198 + 467.2 = 665.2
Total damage combined = 1,449.2

2 Nighttimes hitting with Obliterate.
Nighttime main hand = 484 + 467.2 = 951.2
Nighttime off hand = 302.5 + 467.2 = 769.7
Total damage combined = 1,720.9

So in the example of Obliterate, in equipping two Nighttimes you are effectively putting out over 18% more damage than you would by equipping two Rimefang's Claws.

Rune strike (one of the biggest single target Death Knight threat generators) works the same. It's tooltip say that it "Strike the target for 150% weapon damage plus X. Only usable after the Death Knight dodges or parries. Can't be dodged, blocked, or parried. This attack causes a high amount of threat." The formula for the damage of Rune Strike is 150% weapon damage plus [1/5 AP].

Using the same two weapon sets (2 x Rimefang's Claw and 2 x Nighttime) and assuming the death knight has 1,000AP (to make the math easier) we can see the following:

2 Rimefang's hitting with Rune Strike.
Rimefang main hand = 594 + 200 = 794
Rimefang off hand = 371.2 + 200 = 571.2
Total damage combined = 1,365.2

2 Nighttimes hitting with Rune Strike.
Nighttime main hand = 907.5 + 200 = 1,107.5
Nighttime off hand = 567.1 + 200 = 767.1
Total damage combined = 1,874.6

So in the example of Rune Strike, in equipping two Nighttimes you are effectively putting out over 37% more damage than you would by equipping two Rimefang's Claws.

Clearly there's a big difference between two slow DPS weapons and two fast tanking weapons. For building and maintaining threat, two slow DPS weapons are far and away the best option for dual wield Death Knight tanks -- remembering that threat is equal to damage plus modifiers.

By equipping two fast tanking weapons, as a dual wield Death Knight, you are significantly lowering your threat output. In face roll dungeon runs, when everything dies so fast threat may not be so big of an issue. However, if you ever get to a raid, when all the DPS are pushing the envelope of what they can do, then holding a mobs attention will become more and more difficult.

On the surface equipping two slow DPS weapons that more often than not carry agility rather than strength stats may seem counter-intuitive. It's important to remember though, that in this stage of the game, weapon damage will always outweigh the benefit gained from any stats on the weapon for threat output. Besides, while agility is not something a Death Knight should go out of their way to stack, it's not an altogether wasted statistic, particularly for Death Knight tanks. Agility grants an increased chance to dodge, increased armour, and increased chance to hit with melee critical strikes. 1 point of agility = 2 Armour points. So while a little agility on your weapons is not as good as strength, it's not a big deal, and certainly not a waste.

In a nutshell, because of the way death knight abilities scale with weapon damage and in order to maximise threat for tanking, dual wield Death Knight tanks are far better off equipping two slow DPS weapons and runeforging them with Rune Of The Nerubian Carapace than equipping two fast tanking weapons. By introducing Rune Of The Nerubian Carapace Blizzard gave Death Knights the option of transforming and one handed weapon into a 'tanking' weapon. So head into the Ice Crown Citadel 5 man dungeons grab two [Nighttime], two [Black Icicle] - or one of both - hit the runeforge for Rune Of The Nerubian Carapace, then get back out there and start smacking stuff in the face.

Parting words

Key things to remember, if you are going to dual wield tank as a Death Knight:
* equip two slow DPS weapons (not two fast tank weapons).
* hit 26 expertise
* hit the defense cap 540
* make sure you talent for Nerves of Cold Steel and Threat of Thassarian.