According this spreadsheet by my predecessor Binkenstein, you need about 3,400 mastery rating to get near a point where the buff never falls off. However, that's 3,400 mastery rating with a Lightning Bolt cast speed of 1.5 seconds. With Wrath of Air Totem down and my gear at 2,200 haste rating and a three-stack of the buff (so 2,950 total), I hit 1.55-second cast times on my Lightning Bolt. This means you'd need about 2,400 haste rating pre-stack and 3,400 mastery rating to keep your stacks up permanently, which is more secondary stats than are currently available on our gear.
So kiss goodbye any hope of maintaining a permanent 750 haste stack, but don't let that fact make you think mastery is at all a bad stat. Even with the buff falling off, more mastery means more chances to get it back on quickly and keep your stacks longer; quite simply, more mastery means higher uptime, and this is a very good thing.
Now, there's a bit of a problem with the pro-mastery gearing schema, which is that the majority of caster gear in Dragon Soul is haste-oriented. Haste is available in nearly every spot, and reforging can only do so much for mastery stacking. That said, if you have the time, the valor points, and the DKP, there are some mastery-heavy alternative choices in Dragon Soul.
This is the set
I came up with using only normal mode drops, which simmed at 38,828 DPS and 76% uptime on the set bonus buff. It comes in at 1,550 base haste (and 2,300 with a full stack) and 2,672 mastery. (Fair warning: This set is slightly under spell hit cap, at 1,736 hit rating rather than the 1,742 needed. Going above cap meant slightly losing DPS due to wasted stats.)
- Head Spiritwalker's Headpiece. This is one of the four tier pieces you need for the bonus anyway, and it comes with your two favorite stats, haste and mastery. As a result, don't reforge these at all. The token drops off Warmaster Blackhorn and is most likely one of the first pieces you want to pick up.
- Neck Petrified Fungal Heart, with spirit reforged into mastery. This is one of the only slots where you won't have mastery as a base stat, but since your only alternatives are the crit-heavy Threadlinked Chain and the Opal of the Secret Order, which would leave you even further under spell hit cap, as well as be a waste of your valor points.
- Shoulders Spiritwalker Shoulderwraps, spirit reforged to mastery. This item might seem like a strange choice because the Imperfect Specimens 27 and 28 off Ultraxion are an alternative choice that already have mastery on them, but be confident that there is a method to my madness. Despite the spirit/haste combo on these, they're your second tier choice. The token for these drops off Hagara.
- Cape Nanoprecise Cape, no reforge. The Woundlicker Cover is a great alternative if you need to go resto and share gear with that spec a lot, but Nanoprecise is what you really want due to its mastery rating. Both these capes are purchased with 1,250 valor points.
- Chest Spiritwalker's Tunic, no reforge. Yes, this is the resto chest piece. No, I am not insane. You'll get your four-piece from other sources, and using this chest exchanges a buttload of haste for a significant amount of mastery. If you absolutely refuse to go this route for some reason, you can use Imperfect Specimens 27 and 28 in your shoulders as your off set piece, but know that that will lose you about 60 mastery rating and you'll need to reforge into another 20 spirit somehow. The chest token is from Ultraxion.
- Wrist Grotesquely Writhing Bracers, no reforge. One alternative are the 1,250-valor-point Bracers of the Spectral Wolf, which offer a scary amount of crit rating and have no gem socket, making them no alternative at all. The other choice are the leatherworking Thundering Deathscale Wristguards, which are really nice and really expensive. However, they lack the mastery we're looking for in this set, so the easy to get Grotesquely Writhing Bracers off Warlord Zonozz are my first choice.
- Weapon Rathrak, the Poisonous Mind. No mastery on this, but it still simmed higher than the mastery-laden Visage of the Destroyer, even on single-target fights. This drops off Madness of Deathwing.
- Offhand Weapon Dragonfire Orb, no reforge. Chances are you'll never see this random trash drop off-hand in your life. Even if you do, it will almost undoubtedly go to a caster that doesn't have access to both Timepiece of the Bronze Dragonflight and Ledger of Revolting Rituals. If you can get it, though, it has the most mastery of any off-hand available.
- Relic Lightning Spirit in a Bottle, no reforge. Not only does this relic have spirit and mastery to make it shine, but the only alternative is the Mindbender Lens, which is crit/haste and not worth the valor points for any spec of shaman.
- Gloves Spiritwalker's Gloves, no reforge. Just like the helm, these haste/mastery gloves contribute to your four-piece and have great stats. I actually use these as my resto off set piece too. Token comes from Warlord Zonozz.
- Belt: Belt of Shattered Elementium, spirit reforged to mastery. Because this is a Spine of Deathwing item, it has a higher iLevel than any other belt choice, which means more intellect. There is no comparable choice.
- Legs Spiritwalker's Kilt, spirit reforged to haste. The last tier piece, these come with a large amount of base mastery and some excess spirit to turn into haste. The only other option are the Deathscale Leggings, but they're not really worth spending the gold on and there are better off set shoulder and chest pieces. This token comes from Yors'ahj.
- Feet Mindstrainer Treads, no reforge, 50 mastery enchant. If you have the excess valor points, Sabatons of the Graceful Spirit aren't a bad choice, but if you need the mastery, these boots off Yors'ahj are your best option.
- Rings Ring of the Riven, no reforge, and Band of Reconstruction, no reforge. The first comes from Hagara and the second is a valor point purchase. There are good alternatives, like the valor point purchase Seal of the Grand Architect and the random boss drop Signet of Suturing, and there are bad alternatives, like the crit/hit random boss drop Infinite Loop. None of these have the mastery that Band of Reconstruction and Ring of the Riven offer, though.
- Trinkets Will of Unbinding, Cunning of the Cruel. These aren't related to mastery stacking at all, but no loot list is complete without trinkets, and these are our best choices.
This list should be taken with a grain of salt, as I can't guarantee it's an actual best in slot list. I haven't run the sims of multiple items competing for one slot to see which wins out yet. However, if you feel your mastery is lacking and want to look for upgrades or sidegrades to bring it up, this loot list should give you ideas of where to look first.
Show your totemic mastery by reading Totem Talk: Elemental. Let's get down to business with a heart-to-heart on 4 steps to increase your DPS, choosing a weapon in Dragon Soul, and hot topics for elemental shaman -- or start from scratch by leveling an elemental shaman in the Cataclysm era.