Min-maxing old set bonuses

Small list of tier sets that can still be used even at level 80.
This list is not exhaustive — just what I’ve tested myself.

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Warrior

Tested by me:
T2 (3 pieces): Increases the attack power granted by Battle Shout by 30. Equip 3T2, shout, then equip your main gear. The bonus persists for other people but stops working for you once you swap back.
T6 (2 pieces): Increases the health bonus from your Commanding Shout ability by 170. Works the same way as the T2 bonus.
To get the most out of these, you'll want to spec 5/5 into Commanding Presence.

Not tested:
T2.5 (5 pieces): Increases the slow effect and damage of Thunder Clap by 50%.

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Shaman

Tested by me:
T4 Enhancement (2 pieces): Your Strength of Earth Totem grants an additional 12 Strength. Same process: equip 2T4, drop totems, then swap to main gear. The Strength bonus persists for the raid. It might even work for you, but you don't really need Strength as a Shaman. Also, 3/3 Enhancing Totems is a good talent to have.
T4 Resto (2 pieces): Your Mana Spring Totem grants an additional 3 mana every 2 seconds. The bonus is small, but it’s still something.

Not tested:
T2.5 (5 pieces): -0.4 seconds on the cast time of your Chain Heal spell. This is the same type of bonus as T8, but it's 0.4 instead of 0.2. Probably not worth it.
T2 (8 pieces): When you cast Healing Wave or Lesser Healing Wave, there is a 25% chance the target also receives a free Lightning Shield that deals 50 Nature damage to attackers. If it works, it might be okay to use on tanks before a pull. The problem is the 8-piece requirement; your health and mana will drop significantly before the fight starts.
T3 (4 pieces): Increases the mana gained from your Mana Spring totems by 25%. It likely won't stack with talents (just like the Warrior's T2.5), but it would be interesting to see.
T3 (6 pieces): Your Healing Wave and Lesser Healing Wave spells have a chance to imbue your target with Totemic Power. This proc puts a short-duration buff (8 seconds) on the target depending on their class:
+28 MP5 (Shaman, Priest, Druid, Paladin)
+80 Spell Power/Healing (Mage, Warlock)
+140 AP (Rogue, Hunter)
+700 Armor (Warrior)
Good on paper, but again, it requires too many gear swaps. Also, I wonder what kind of buff a DK would get.

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Just two classes for now. I will add to or edit this post as I test more sets and have more time.

here's one i saw from a resto druid in a 5-man VH: 8/8 tier 1 (from Molten Core) for -50% reduced CD on Tranquility + specc into "Improved Tranquility" on your resto spec for another -50% reduced CD = the spell will have 0 CD. It's literally spammable. Idk about its interaction with Omen, but every time this guy casted Tranquility his mana wouldn't go down (Tranquility possibly has a very high Omen proc rate).
In theory, you can have any number of resto druids in a raid 25-man raid group, possibly each assigned to a group, and just ignore most mechanics with the HPS they provide (highest HPS in the game bar none).