I'm trying to reach 4set bonus (with 264 pieces), but it isn't easy for me. First, T10 chest doesn't have any def rating and using Pillars at the same time (also no def rating) would put me below 540def. But it isn't very big concern, cause I'm hoping to change boots (currently no def rating either) and get around this problem.
What's worrying me most is that T10 pieces have less sockets than my current gear (which is also 264lvl). I would loose 3 sockets in total. So the question is: Is T10 4set bonus worth 3 sockets?
4 piece cooldown is very handy for fights like Saurfang, Fester (although IBF, trinket and glyphed VB have been enough for me in the past during inhales), Sin and LK. Other fights where you aren't facing potential <1.5 second deaths may see more benefit from the EH stacking.
With your defense, keep in mind you get .16% crit immunity from the pvp enchant.
I've found it hard to justify the 4pc bonus while sacrificing the awesome 264 badge gear. My favorite on any tank toon has been tier head & shoulders, offset chest & hands, crafted pants. That usually gives the highest EHP without access to 25man loot.
If you REALLY wanted the cooldown, i'd go with head, shoulders, chest & hands. The chest & hand tier pieces have extra armor to help with the EH so you lose only a little, while keeping the excellent crafted legs.