Shiekyerbooty, I'm guessing you loaded your character in with the default stat weights, which are good for T14 gear and early T15 gear. You have the Legendary Meta gem and some nice gear, so you should be using the T15 weights. Once you switch to those weights, Mr. Robot recommends Haste over Mastery. I must note that I found a typo on the 'short description' of the T15 weights: it incorrectly says Mastery > Haste, but the stat weights are correctly weighted as Haste > Mastery. So don't let that confuse you (and I'll be fixing that typo asap).
Here's a saved profile with the T15 weights:
http://www.askmrrobot.com/wow/gear/f...9-a85b73ed12f2
I simmed it, and it does in fact do more DPS than your current setup. It's close, but still better by a bit.
Xuros - can you tell me what your character sheet HIT says in-game? Is that what you were looking at, or were you looking at the armory? In the past, battle.net wasn't adding expertise into your hit score. I don't know if that's been fixed or not - but in-game was always showing it correctly. Let me know what you find and I'll dig into it some more if necessary.