There's a reason that you can't sim it. That weapon is terrible for enhance shamans for a number of complex reasons (though I won't clog up this forum with them). To answer a simple question with a simple answer:
Enhance shamans should be dual-weilding as soon as they hit level 40. You should try to get two weapons as close to 2.6 or 2.7 speed as you can.
And lastly, that axe really isn't itemized for shamans. Strength and Armour Penetration aren't optimal stats for Enhance Shamans.
If you'd like to learn more, go to the Enhance Shaman Theorycrafting Think Tank link. It's easy to read, and has all the basic information (and more) that you'll need to gear up your toon effectively.
Here's the link:
Shaman: Enhancement