Historically, "slower is better" has been a staple of rogue weapon selection. Going all the way back to two best-in-slot items, Teebu's Blazing Longsword and the Barman Shanker, we can see that even a 0.1-second difference was enough to tip the scales. While there have been several changes to rogue mechanics in the years since Molten Core, the most drastic changes to rogue mechanics were the recent poison updates. Most of our percentage-chance poisons were moved to a proc-per-minute (PPM) mechanic, shifting the entire paradigm of how we look at weapon speeds.
Deadly Poison forces one quick weapon
Deadly Poison had been designed poorly since day 1, as it was a refreshing DoT with no application effect. It wasn't until Adrine and the PoisonSwapper addon that this was brought to the public's attention and Blizzard was forced to react. The newly implemented Deadly Poison/opposite poison proc chance changes the way we think about weapon speeds and poison selection. Due to the fact that Deadly Poison was left on a pure percentage-chance proc rate, we require a quick weapon to be used. As a rule of thumb, any effect that has a flat percent chance to apply favors a faster weapon. No matter what spec you're currently using, you need at least one quick weapon for Deadly Poison application and maintenance.
Of all rogue specs, combat has the most specific weapon speed requirements. Combat rogues probably know where I'm going with this already, but basically the entire combat energy regeneration system is based off the talent Combat Potency. The quicker the weapon, the more energy you will recover. As this talent is crucial to combat rogues' scaling properly with haste and haste effects, we're forced to use the quickest off-hand possible. That's OK though, because we already needed to use a quick weapon for Deadly Poison, so we simply combine the two and use a quick off-hand weapon with Deadly Poison on it at all times.
For our main-hand weapon, we're looking for the slowest weapon possible. Even after the instant attack normalization of vanilla WoW, slower weapons are still better for combat in the main hand. Our Sinister Strikes, Eviscerates and Killing Sprees have a chance to proc a poison, so having a slow weapon makes the PPM system work for us. What's nice about combat is that we can also use both swords and axes, which means that any slow or fast axe or sword can be used. While maces and fist weapons are an option for combat, those weapon specializations fall behind Hack and Slash in terms of potency. This is going out the window in Cataclysm, but that's still pretty far off on the horizon.
If you're an assassination rogue, then you understand how important your poisons are to you. Without Deadly Poison, your Mutilates would feel like a swing from a foam bat. Without Instant Poison, your Envenoms would lose their powerful secondary effect. Poisons end up being a large percentage of your overall damage, and so optimizing your weapons to maximize their effect is key. It's why assassination rogues don't stack armor penetration and even do things like gem for haste. The quicker that a five-stack of Deadly Poison is active, the better. Their primary energy regeneration mechanism, Focused Attacks, is a percentage-chance proc and favors quick weapons as well. Coupled with the Deadly Poison requirements, it becomes obvious that mutilate rogues require at least one very quick dagger to function properly.
We know that assassination rogues will want at least one quick dagger to satisfy the Deadly Poison weapon requirement, but what about the other dagger? It actually turns out that the speed of the second dagger is not as important as the speed of the first. Slower daggers yield a better poison proc rate on instant attacks and stronger Mutilates, while faster daggers generate more energy for us to use. The difference between two similar daggers with different speeds is actually incredibly low, so find one quick dagger and then any other. In PvP, this paradigm shifts a bit, as stronger Mutilates are key to having the burst necessary to kill a target. Deadly Poison is also less valuable, as it takes time to stack up and can be dispelled. Two slow daggers are perfectly fine for PvP use, though I see many rogues favoring the slow/fast dagger mix so that they can use their weapons in both PvP and PvE.
The issue is if you have two good-quality slow daggers and only bad quick daggers. What do you do in this situation? I'm sure you can guess: spreadsheet it. I will tell you that a quick dagger from last tier will typically outperform a slow dagger from the current tier, when we're talking about the dagger with Deadly Poison on it. Unfortunately, there aren't a ton of quick dagger options available without raiding, and Blizzard has a penchant for placing them on later bosses like Professor Putricide. Combat, on the other hand, can find amazing weapons in both 10-man and 25-man versions of ICC from the first four bosses. I have seen a lot of raids initially dole out their quick daggers to rogues on a "one each" basis, so that every rogue will have at least one speedy weapon for Mutilate. Later on, once everyone has a quick dagger, they can go back and pick up a second one if desired.
Keeping us on our toes
With the upcoming changes to haste and energy regeneration in Cataclysm, I am fairly certain that talents like Combat Potency and Focused Attacks will see significant modification. Which weapon speeds are desirable for which specs can change with even the simplest change, so Blizzard can keep us on our toes as they refine the rogue class. What's important is to understand why we choose the weapons that we do, so that we have a better understanding of how our class works. The more you know about the class, the better rogue you will become.
Are you a rogue looking to up your game? Check back every Wednesday for the latest strategies in Encrypted Text! Get ready for Icecrown Citadel with our guide for rogues, part 1 and part 2 (Plagueworks), part 3 (Crimson Halls) and part 4 (Frostwing Halls). Just hit 80 and need information? Check out our rogue lessons: Combat 101 or Mutilate 101 for all you need to know to get started.