If you are in a position to grab the optimal heirloom items for elemental, you will rock 1-80. Especially pre-outlands when there are so few options for casters, and shamans in particular. Unless you really, really like spirit.
The best heirloom options for elemental shamans
Mystic Pauldrons of the Elements
The PvE shoulders are superior to the PvP alternative, even for PvP.
Mystical Vest of Elements
Fabulous for the leveling shaman, particularly pre-Outlands. Pop a +4 all stats enchant on this if you like.
Weapon - 2H
Dignified Headmaster's Charge
If you roll a lot of alts, you will get multiple uses out of this. It's a better choice than the mace because there are no heirloom off-hands or shields.
Discerning Eye of the Beast
You're unlikely to find an upgrade for this before you hit 80. I would pass on the other trinket but go ahead if you have extra emblems.
If you have cloth or leather caster heirlooms already, feel free to use them instead. Otherwise, go for the mail pieces. They are designed 100% for elemental shamans but can't be shared by any other alts, except possibly a holy paladin.
I leveled as elemental using the enhance/hunter heirlooms (agility & AP for the win) without any problems. It doesn't really matter what gear you wear. The 20% exp bonus is yummy so as long as you have the chest and shoulders, regardless of type, you will level fast.
Shamans scale extremely well with their talents, spells and totems, even naked. The problem shamans face come in deep endgame when other classes scale much better with new gear.