Never, ever, ever, ever, ever, ever, ever, ever, ever use mage armor. Ever. It gives a flat 3k rating, whereas haste is giving a 7% multiplicative bonus.
You would be better off reforging to mastery, or gemming mastery, before switching to mage armor.
Since you have Black Blood, and if you would prefer to use that but feel as though you'd like more mastery, then can gem for it instead. Your gear isn't too far off from what I was wearing in normal modes, and I just kept stacking haste. At one point I was over 20k and I enjoyed it. Now with some heroic pieces I'm down to just above you actually and while my single target is higher, I was multidotting better when I was in normal gear :P
I really want everyone to realize that just because your frostbolt dips below GCD doesn't mean haste is suddenly bad. That's what I prove in this guide. You spend more time outside burst haste scenarios than you do within them, especially with icy veins glyphed. It might feel weird, but that's only for a small portion of the fight. For the rest of the fight it's quite nice having such rapid casts. As you increase your ilvl and mastery + haste increases, you're generating icicles fast, bombs are ticking fast, and everything is just glorious.
Here's me running w/17678 haste & 12291 mastery. Our first Heroic Malkorok kill:
http://worldoflogs.com/reports/rt-pi...?s=1079&e=1393