This post will give details of what Spell Hit/Hit Rating is required for each class vs bosses (mostly 10man and above), as I often get asked this question in game.
nb. Dual-Wielding melee classes' Hit requirements are slightly more complex, and are mentioned at the end of this post.
Importance of Hit Rating
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If you are not Hit Capped (maxed out Hit Rating for PvE content), then +Hit is the most important stat in maintaining acceptable DPS in a raid.
Once you are Hit Capped, you can then focus more on your other relevant stats. nb. The stat priority is different for each class after the Hit Cap is reached.
Class DPS Hit Rating Requirements
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Druid Melee: 142
Druid Spell: 202
Talent bonuses:
152 with Balance of Power talent
Hunter: 142
Talent bonuses:
95 with Surefooted talent
Mage: 202
Talent bonuses:
164 for Frost and Fire spells with Elemental Precision talent
76 for Arcane spells with Arcane Focus talent
Paladin Melee: 142
Talent bonuses:
95 with Precision talent
Paladin Spell: 202
Talent bonuses:
164 with Precision talent
Priest: 202
Talent bonuses:
76 for Shadow with Shadow Focus talent
26 for Mind Blast alone with Shadow Focus and Focused Mind talents
152 for Mass Dispell, Smite and Mind Blast with just the Focused Mind talent
Rogue: 442 (for Dual-Wielding*)
363 (for Dual-Wielding*) with Precision talent
Special Attacks: 142
63 with Precision talent
Shaman Spell: 202
Talent bonuses:
126 withonly Elemental Precision talent
164 with only Nature's Guidance talent
88 with Elemental Precision and Nature's Guidance talents.
Shaman Melee: 442 (including Dual-Wielding*)
Talent bonuses:
348 with Dual Wield Specialization talent.
395 with Nature's Guidance talent.
300 with Dual Wield Specialization and Nature's Guidance talents.
142 for Special Attacks or 95 with Nature's Guidance talent.
Warlock: 202
Talent bonuses:
76 with 5/5 Suppresion talent.
nb. Suppresion only applies to Affliction spells, so it won't benefit your Destruction spells (Shadowbot, Immolate, Soulshatter, etc.) at all.
Warrior: 442 (for Dual-Wielding*)
Talent bonuses:
395 with Precision talent.
2handed/Special Attacks: 142
2handed/Special Attacks: 95 with Precision talent.
*Melee that Dual-Wield have such a high Hit Rating cap that common sense is the best way to view your stat needs; never totally disregard Attack Power, Strength, etc.