shield slam > revenge > shockwave > conc blow > devastate.
There are several different hit caps.
The melee hit cap causes all your single weapon auto attacks to always hit and causes all special melee attacks to always hit. This is reached at 8%.
The spell hit cap causes all your spells to always hit. This is reached at 17%.
The dual wield hit cap causes all your dual wield auto attacks to always hit. This is reached at 27%
Hit is almost a pure threat stat, it causes your attacks to hit more, and thus it makes you do more threat. There should be a reasonable amount of hit available on tank gear, but you shouldn’t gem or enchant for it.
The only time you should ever worry about hit caps is if you need to taunt something. If you glyph taunt, and the boss is properly debuffed (Improved Faerie Fire – Spell – World of Warcraft or Misery – Spell – World of Warcraft), you need 6% additional spell hit chance to always hit with yout taunt. This is 158 hit rating.
Note that taunt is based off of spell hit, and that you get more spell hit chance from your rating then that you get melee hit chance.
Expertise governs two things. The chance a mob has to dodge you and the chance a boss has to parry you.
You negate the mobs chance to dodge you when you reach 6.5% dodge and parry reduction at 26 expertise skill.
You negate the mobs chance to parry you when you reach 14% dodge and parry reduction at 56 expertise skill.
A note on hit and expertise.
For both hit and expertise, the general thing to remember is this: “If you do enough threat, you don’t need more of them. It is important, though, to realize that having more of either of them will make your threat less spiky. While this effect is minor, having a string of misses at the beginning of a fight can cause someone to grab aggro.
My advice would be to not worry about getting to either cap, but not completely ignoring the stat either. Gemming or enchanting for hit or expertise shouldn’t be needed