The T7 guide for gear will be out either later today or tomorrow, and should be a fully integrated guide with the other one so you won't have to swap back and forth. Which...is why it's taking a bit longer. :)
This is an addendum to that guide and the other ones I've written. And that addendum is: the polar gear ( Polar Boots, Polar Cord and Polar Vest) are not as good as the guides say.
And yes, they have a TON of stamina.
If you go by Rawr right now, these are either best in slot or damn close to it - especially for pre-naxx gear levels. And Rawr encourages you to put as much stamina in there as you humanly can. With those three items alone, you can have 595 stamina (assuming 24 stam gems). And that sounds awesome, right? Except it has no avoidance, no AP, no crit, no expertise, nothing. Same with my rating system - polar gear comes either on top or close to it.
But that's not quite right.
Now, at level 213 the Polar gear is definitely good starting material. There really aren't that many good chests that you can get pre-Naxx, and you can very easily make it a good basic chest - with 169 stam and 48 agility, for instance, it's pretty sweet. But it really isn't the best overall thing you could get (which is what my rating system would say) or close to the best (what Rawr says). Let's compare the Polar Vest to something similar (and not horribly hard to get): the T7.10 chest. The Naxx (and emblem) chest loses a socket and 80 stamina, straight out of the gate. Sure, it has potentially 56 more agility, but 56 more agility to 80 stam?
Yeah, that's actually a pretty good trade.
Why? Because you really don't need a trillion stam to tank in Naxx. There are two fights where stacking as much stam as humanly possible makes sense: Malygos's breath (where you can take 30k damage before reductions) and Sartharion + 3 adds (where you can take 35k-39k depending on whether or not you're debuffed in a certain way).
And that's it. And if you're raidbuffed, you can get that easily, in your sleep, if you have proper gear. Heck, that's just the agility; you'd also be giving up 132 AP, 54 crit and 35 expertise.
What about the Polar Boots? Well, compared to the Slag Footguards, you're losing 30 agility for 70 stam. That sounds like a bad tradeoff, save that stam doesn't matter so much and you'll be gaining some threat. For the belt it's worse - only a 51 stamina vs 30 agility difference and you'll lose about 130 AP and 30 expertise (assuming you're going after the Sharp-Barbed Leather belt, the best belt pre-or post-naxx save PvP gear).
Like I said - all of these things are viable. They're just not 'best', and don't let that huge stamina and people in LFG fool you - having a 40k health pool when you have 25% avoidance is a recipe for a really unsatisfying PUG.