Personally, I have mixed and matched both PvP and Arena with the gear from 5mans and Karazhan (read the BBW head).
Netherstrike offer a nice Mana/5 boost if you want that... although with the recent changes to Water Shield, Elemental Focus, and the Mana Stream totem... the mana/5 issue is really becoming less of one.
I also agree with the posts about the wrists, belt, sabatons, and weapon. Those pvp-non-set epics are amazing pieces, and while they only offer one gem slot between the three, they are excellent pieces that you can get only better of out of heroics (read Wave-Song Girdle), heroic badges (read Treads of the Booming Thunder) or raiding drops (read that as things like the Hurricane Boots). Even then I would argue that the PvP options are better still. In the weapon department, while there is a weapon out there, the Runesong Dagger, with crit and damage, the damage is only 121. Also, there is a dagger out there with hit and damage, but it is from a heroic, and is still only 121 damage. The s1 caster weapons while not having hit or crit on them, have a phenomenal 199 damage, and are a great choice. I highly recommend getting one asap, since it saves you the problem of having to run through SH repeatedly trying to get it.
I do not agree wholeheartedly on the Tidefury set... I've rarely seen these pieces drop even on multiple runs per day of the instances including only seeing the chest drop once, but also, the statistical differences are not that much over the pvp gear.
Tidefury bonuses: 30 Int, ONLY 10 hit rating (0.81%) contrary to the above post praising the hit rating... , and only 4mana/5 without the extras of the bonus set. I will admit that it is nice to have that Chain Lightning drop reduction of the two piece Tidefury, but I also have not had the 4pc bonus after patch 2.3. If it is true and the subsequent mana refund is an extra 168 mana higher, that would further help out if you have constant mana problems by giving an extra 7.5 mana/5.
Gem bonuses of Tidefury: 3 yellow, 2 blue, 1 red, 1 meta. Meta selection is slim and is the same whether for this set or Thunderfist, and blues are usually some mix of stam, leaving with one red spell damage and 3 spell crit (read that I am going color specific, if you choose not to go color specific it doesn't matter the color of the slots anyway).
Thunderfist bonuses: 81 stamina, 85 crit rating (almost 4%), and 14 damage. The 4pc bonus is nice for instances where you have auras up, such as Mechanar, or if you do have to offtank something or solo kill a caster in places like Shadow Labs with the locks and pets in the refectory. Also, this is the only place you'll find an interruption reduction for elemental spells.
Gem bonuses of Thunderfist: Three red, three yellow, 1 meta. You have the option of going all spell-hit/crit/damage based in the two color slots, instead of Glowing Nightseyes in the blue sockets or adding in a Talasite with spell penetration.
If you are interested in joining the 5v5 group, you want stamina, crit, and resilience. You will achieve an extra 81 stamina, 4% crit, and 125 resilience increase with the so-called 'welfare gear'. If you want to PvE, the gladiator gear will serve you just as well as the Tidefury, apart from being more expensive to repair.
I disagree with Gaudion on the gear itself. I think the non-gladiator gear is a phenomenal place to start, but I think you would be fine with either s1 or Tidefury, I would choose s1 personally. Spell crit is not the only thing for an elemental shaman, but it is the most important thing. 4mana/5 and the water shield bonus versus the crit boost is a personal decision, but with the 172 mana/5 outside of casting and 62mana/5 while I currently have in addition to the Water shield and Mana Stream are enough to keep me going through very long cases of boss fights even when I am moving totems and spot healing.
Also, on a personal note, while I do not mind running instances trying to get pieces of the Tidefury to drop because it helps my guildies get geared, it does drive one absolutely bonkers when you are going through your fourth or fifth set of people and you're still waiting for the second piece to drop. S1 gear you know exactly how to get it, and a good day's worth of pvping can net you a piece of s1 gear.
Congrats on the 70 ding too.
Good luck and happy hunting.
Cheers!