Gear designed for assassins like us can have a variety of stats. Haste rating and armor penetration are among the fringe stats that are simple DPS increases without any sort of "cap" to achieve. Agility and its base components of attack power and critical strike rating are always awesome; but again there is no magic bullet when balancing these numbers. The two stats that you WILL want to focus on when you choose your gear for Naxx are hit rating and expertise rating.
As has been the case since level 1, increasing your chance to hit (or inversely reducing your chance to miss) are the purest ways for a Rogue to increase his or her damage. Hit and expertise scale with every other stat, making them the obvious candidates for gems and enchants until you've reached their caps. Let's talk about the current hit caps that a Rogue will face.
While Adrine of Cenarion Circle has compiled a great (and thankfully stickied) post containing all of the hit cap numbers for Rogues at 80, I'll go over the key values from that thread. Any Rogue PvE build must contain Precision. Every value that I give for the rest of this article will assume that you have 5/5 Precision in your build, regardless of whether you are HaT, Combat, or HfB Mutilate.
A raiding Rogue with Precision will be shooting for 99 hit rating as a bare minimum from gear (66 if you're playing with a Draenei). This is ensures that all of your yellow (special) attacks will hit (provided you are also at the expertise cap) and is easily achieved with a few +hit gems and possibly a precision enchant to your gloves. Reaching the Yellow Hit Cap (YHC) is crucial for maintaining your rotations.
The next hit cap that a Rogue will shoot for is 315 hit rating (237 with a Moonkin or Shadowpriest, and 210 with a Draenei as well). This is referred to as the Poison Hit Cap (PHC). At this point, bosses will no longer be able to resist your poisons, which is another huge DPS increase. Hit rating now works on both melee attacks as well as spells (which our poisons are considered to be). Reaching the PHC should be your primary focus once you've reached the YHC and the Expertise Cap (EC).
White Hit Cap:
The White Hit Cap (WHC) was a stat that Rogues would previously shoot for in vanilla WoW and TBC, specifically due to the fact that such a large portion of a Combat Rogue's damage came from white (auto) attacks. Now that Mutilate and HaT are in vogue, as well as the fact that poisons now make up a significant portion of our damage, reaching the WHC is not only irrelevant: it's nearly impossible without gimping your other offensive stats.
Expertise reduces your target's chance to dodge or parry your attacks. While I have been heralding this as an amazingly underrated stat, raiding Rogues have been ensuring that they reach its cap, the EC. Bosses can still dodge attacks coming from behind them, and so by removing their chance to dodge from behind, you again ensure that all of your attacks land as planned. The amount needed to remove a boss' chance to dodge from behind is 26 Expertise, or 214 Expertise Rating (Humans will have slightly reduced amounts required). This should be your first priority once reaching the YHC.
Putting it together:
To summarize, a Rogue's priority for stat caps should be: YHC (minimum to even run a raid or heroic), EC (well-rounded Rogue), and finally the PHC (raider status). After reaching all of these plateaus, it becomes time to start gemming for pure DPS stats and focusing on increasing your attack power and critical strike chance. Until you reach the EC, your gems and enchants should all be hit or expertise (where applicable). The value of hit rating and expertise rating trump all other stats before you reach the YHC and EC.
While reaching some of these stats may seem difficult, there are a few key items that will allow you to reach these caps very quickly. For example, combining the BoE Chain Gang Legguards and the easily acquired Sphere of Red Dragon's Blood (I talked about this earlier), you've already reached the YHC from just two items. Similarly, the BoE crafted Trollwoven Spaulders and Girdle will get you well over 25% of the way to the EC and are very nice pieces of gear in their own right. I'm still using mine!
Theorycraft it anyway:
While the advice given in this column will apply to most Rogues and most pieces of gear, there are still a few caveats. If you are upgrading from a level 75 blue stacked with hit rating to a level 80 epic with no hit rating whatsoever, it still may be beneficial to wear the epic anyway. While below the YHC/EC/PHC the value of hit and expertise are very high; but sometimes not high enough to offset the difference between a blue and an epic. Put both pieces into a spreadsheet and see which comes out with a greater damage increase.
You may be seeing a lot of our brothers and sisters of the shadows advertising in Dalaran that they are "hit capped" and looking for a raid. In reality, as it's impossible to reach the WHC realistically, they're likely talking about the YHC or the PHC; and which tier they're at makes a big difference. Once you've reached the YHC and EC, you'll be ready to raid full time. Next week I'll be covering the gear that you can use to reach these caps and to ensure you are prepared for Kel'thuzad and his acolytes.