Critical strike is nobody's favorite
If you've been following any rogue resource, you know that critical strike rating is the worst stat for every talent spec in PvE. Assassination used to enjoy bonus energy via Focused Attacks when crits landed, but that talent is no more. Combat had a similar crit-strengthening talent in Prey on the Weak, but PotW is also missing in Cataclysm.
It's not that critical strike rating doesn't increase our damage, because it clearly does, but it's simply not worth the investment. We're playing in a world where a simple DPS increase isn't enough, where we can pick and choose only the best stats. The upside of crit is that by having one stat that's clearly the worst, it makes many of our reforging decisions very easy.
Mastery reinforces spec stereotypes
While assassination and combat haven't really ever had identical stat valuations, mastery rating tweaks our damage makeup and pushes them further apart. Assassination's mastery bonus increases its poison damage, which makes stats that also boost poison damage incredibly valuable. Combat's mastery bonus increases its physical damage, which promotes physical stats over the others.
The synergy that's seen between mastery and the other stats simply reinforces the stereotypes of Mutilate's heavy poison damage and combat's primarily physical damage. That's actually one of the purposes of mastery: to create noticeable differentiation between specs.
Expertise is the ultimate boost to physical damage
Expertise rating reduces our opponents' chance to dodge or parry our attacks, which makes it great for boosting the number of white swings that land. Combat, which favors physical damage and white swings, obviously loves expertise. A combat rogue needs for as many of his swings to land as possible to generate Main Gauche and Combat Potency procs, specifically because they're percentage-based procs.
Assassination, on the other hand, couldn't really care less about expertise. One key reason is that a Mutilate rogue's key finisher is Envenom, and Envenom actually still grants you the poison buff even when it fails to land. Between Envenom's indifference to dodges and assassination's reliance on poison damage, expertise simply fails to be a good stat.
Hit rating is universally loved
Hit rating increases both our chance to hit with both physical attacks and spells (which poisons are considered to be), making it valuable for both specs. Every rogue wants to reach the basic yellow hit cap, as we need for our special attacks to land in order to maintain a rotation reliably. Even after that point, both combat and mutilate value reaching the spell hit cap quite a bit, which is why it's such an easy stat to love. The only issue is that hit rating has almost no value past the spell hit cap, and since we can easily reach that golden 17% hit chance between Precision and current gear, it's not always in demand.
Why haste is twice as effective
Back in the day, haste's purpose was to increase the number of white attacks a rogue could perform. While Focused Attacks and Combat Potency allowed for haste to boost our energy regeneration, it wasn't the primary function. Haste now directly increases our energy regeneration, allowing it to boost both our yellow and white damage. It's valuable to both combat and assassination due to its dual-nature, which makes it universally valuable. By having a few stats that one spec prefers and a few stats that both specs love, gear decisions can become more interesting than simply stacking armor penetration.
I've seen a few rogues talking about a "cap" on haste, even though there's no such thing. While stacking haste and using Adrenaline Rush during Bloodlust might have you generating more energy than you can spend, there are ways to avoid this situation. Staggering Adrenaline Rush to ensure that it doesn't intersect with Bloodlust is one technique, while ensuring that we don't use Killing Spree while at nearly full energy is another.
No matter how much haste you stack, you simply can't get enough to passively cap your energy regeneration. Haste doesn't have any diminishing returns, either, and we can always feel safe adding more to our gear. If you're running into a situation where you have too much energy, you should find a way to adjust your playstyle to account for that energy surplus. Reforging out of haste to lower your energy regeneration isn't fixing the problem and causes another by lowering your overall DPS potential.
Hit the caps, then stack mastery and haste
Only hit and expertise are considered to be stats with caps, and it's because of a boss' chance to dodge, parry, or be missed by an attack. We're left with mastery and haste as the stats that scale out forever. Critical strike rating actually does have a cap, as we experienced in Icecrown Citadel gear, but since it's so bad, we won't be stacking it enough to reach that cap any time soon. Assassination rogues start stacking haste and mastery as soon as their spell hit cap is reached, while combat does the same after reaching the expertise cap.
The progression of capping the basic stats of hit and expertise and then pushing for the infinite stats has been happening forever, and that should stay the same throughout the rest of Cataclysm.
Check back every Wednesday for the latest rogue strategies, from rogue basics and kicking your interrupts into high gear to how to handle your dual-spec rogue and how to pickpocket top tips from top-performing rogues.