I ran your numbers through
harlekin's Dodge vs Defense Calculator using +16 Dodge Rating Gem. Here are the numbers:
Currently
736 Defense Rating
19 Parry Rating
143 Dodge Rating
112 Agility
Neck Change
+5 Defense Rating
+32 Dodge Rating
(
21.68 Total Avoidance (+.71))
+12 Stamina
Waist Changes
+2 Defense Rating
+32 Parry Rating
+8 Dodge Rating
(
21.66 Total Avoidance (+.69))
+1 Stamina
+43 Armor
TL;DR
You are looking at inSANEly similar Upgrades here. In this situation, I would make your choice based on the likely hood of receiving comparable upgrades from other sources. Since a glance over my personal loot listings (my gear situation is fairly similar to yours) shows no other upgrades before Naxx-10/25, that doesn't help the decision.
Based on the fact that the necklace uses Dodge, rather than Parry, to upgrade your Avoidance, and also has the additional Stam boost. I'm tempted to say to get that. However, I'm going to recommend the
Waistguard of Living Iron as your choice. The reason I say that is, you can get a belt buckle and gem put on the Waist piece. Yes, this may require a small monetary investment, but there's almost no time investment required, and this belt will be with you through part or all of T-7 (randomn loot is randomn) so it's a wise investment to make and there is not reason to put off this opportunity to increase your stats.
TL;DR
get the belt
Waistguard of Living Iron and put a buckle on it.
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