Well strength is almost completely ignorable as a defensive stat, it's really 10 agility versus 175 health on the chest part, which is drastically swayed in the direction of the raw health.
Really the same thing with the 30 stam shoulders versus dodge/defense.
The biggest upgrade for you from Frost Emblems would be the Corroded Skeleton Key over Essence of Gossamer, then probably the Belt over your current Belt, assuming you get the cloak I am about to link. It is easily obtainable from the Frost Lord Ahune fight - http://www.wowhead.com/item=54801.
The Black Heart comes from a 5 man dungeon.