Deciding what to buy with the EoFrost can be a pain in the butt. When figuring out what is better to get first, it is important to remember your hit cap. I play Horde side and know that I almost always run with a Boomkin who can provide extra hit with his FF, so I sit at around 289 hit rating. If you don't have a regular Boomkin (or Shadow Priest), you should be sitting at around 368.
I started by prioritized upgrading items that do not currently have Hit rating on them so that I am never losing Hit rating in an upgrade. I also looked at what else was added in 3.3 as far as drops go to see if there was anything useful I could get from raiding. Items which were exclusive to badges were placed higher. Then of course was the amount of an upgrade the item is.
So without further ado, here's the order I'll be buying stuff with EoFrost:
1. Frost Witch's Shoulderpads (aka T10 Shoulders) - No matter if you're sporting your T9.5 Shoulders or the crazy odd Heroic Pauldrons of the Glacial Wilds (like me), these shoulders are a step up even at the 251 iLevel. One thing to consider at this point are your set bonuses. If you only have 4 of your T9 and one of them is your shoulders, then you will also be losing your 4P T9 bonus and not gaining your 2P T10 yet.
Cost: 60 badges
Total Badges spent: 60 badges
2. Frost Witch's Helm (aka T10 Helm) - Another clear upgrade from the T9.5 Helm, even at the 251 iLevel. A slight loss of Haste (4 rating) is all you'll see from this upgrade with gains everywhere else. You will break your 4P T9 at this point, but also pick up your 2P T10.
Cost: 95 badges
Total Badges spent: 155 badges
This is where my path diverges. I'm aiming for this set of gear. The Amulet of the Silent Eulogy and the Loop of the Endless Labyrinth are both drops from 25man ICC and contain Hit. Depending on if I have either (or both) of those and my hit is still ok without gemming for it, will determine what I buy next. Basically, if at any point from here I need to gem for Hit...I'll buy the Belt of Omission (Cost: 60 badges) to boost my current hit.
3. Frost Witch's Kilt (aka T10 Pants) - This is the first piece that will come with a Hit rating loss. At only minus 10 hit rating compared to T9.5 Pants though, it is an easily manageable loss (hybrid hit gem negates till other hit items are acquired). Depending on what you already had and what you've replaced, this may break your 2P T9 without gaining 4P T10. If you started with 4P T9 and bought the T10 piece you didn't have first (going 4P T9, 1P T10), then you will be 2P T9, 3P T10 at this point.
Cost: 95 badges
Total Badges spent: 250 badges
4. Frost Witch's Hauberk (aka T10 Chest) - This will round out T10. It is also a large loss of Hit (85 Rating) compared to the T9.5 Chest. If the RNG has been cruel, swapping in the good old Elemental Focus Stone for the transition may be needed.
Cost: 95 badges
Total Badges spent: 345 badges
5. Blizzard Keeper's Mitts* - These are nicely itemized gloves for Elem and the Hit loss over the T10 Gloves can be made up elsewhere. Also, because of how the T10 items are bought you need to spend the same amount of Badges on either of these gloves, but you also need a Token for the T10 to make it equivalent to the Blizzard Keeper's Mitts. That sacrifice has been made on other slots in order to get the 4P T10.
Cost: 95 badges
Total Badges spent: 440 badges
6. Bizuri's Totem of Shattered Ice - You may be asking yourself why this is so low on the list. My answer is that if you have Totem of Electrifying Wind (which if you don't, you can easily get from EoTriumphs) then you only gain 20 haste from this upgrade. There are other trade offs as well, but you should be using Lightning Bolt enough to keep the ToEW proc rolling.
Cost: 30 badges
Total Badges spent: 470 badges
At this point I may purchase Maghia's Misguided Quill to use when the resident Boomkin is not present. This far down the list, there's not much else to buy.
I also originally had Drape of the Violet Tower listed. While it's a good cloak, it is more for healing than DPS. I feel I could do better with Shroud of Displacement, but I'll have to rely on the RNG for that.
And there you have it. A list of the EoFrost purchases, and then some.
*I feel I must explain my choice of omitting the T10 Gloves. The BKM gloves are well itemized for Elemental and the Hit can be made up elsewhere. The goal is 4P T10. There's no good substitute for T10 Helm, so that's one. Shoulders have a good option with Horrific Flesh Epaulets, but they are basically equivalent and depend on a specific drop from Festergut 25man. Chest has the option of Meteor Chaser's Raiment which is also purchasable for 95 badges. This is a harder choice as technically the non-tier would offer 16 Haste and 12 SP (if you gem the extra slot for SP) while losing 24 crit. But it's a Cloth robe and looks horrible imo, and yes I'm vain enough to say that. Lastly we come to the Legs, the other contender for replacement. If you have deep pockets, you can opt for Leggings of Woven Death crafted by a Tailor using 8 Primordial Saronite (Taken over the comparably crafted Lightning-Infused Leggings because of the Haste for Crit trade), or there is the Plaguebringer's Stained Pants which is better because it dumps all the crit for Haste and keeps the Hit. Good luck getting them though since 1. They Drop from Festergut 25man and 2. they are cloth, meaning most likely Mages, Locks, and SPs will have priority (rightly so imo).