I think the reason Agi outperforms Str in 3.1 is due to the Primal Gore talent allowing the periodic damage from Rake, Lacerate and Rip to crit. Since Agi increases our crit chance it becomes the more sought after stat.

Your armor value seems high for a pre-inspiration 3.1 value. Or is this 3.0.9?

After. Pre 3.1 is around 38k.

SR improved crit scaling before, the only real change is primal gore greatly increasing agility scaling and the SR change decreasing ap/str scaling by ~3 % (including the glyph).

Bear questions....

Why does haste have a negative value? Doesn't more attacks mean more SD procs?
What exactly does "Night's Choice" mean? IOW, why did you inflate some values over those in the first column (like hit)?

I'm guessing haste has a negative value because it increase parry gibs.

Night's Choice is my personal stat choice, if you want to know how is build is the following:

70% Stamina-equivalent tankpoints + 30% ap-equivalent TPS. After that I've inflated by 20% hit an expertise and reduced by 10% ArPen. Reason for those changes: hit it's the best threat stat (after expertise) because make it stable, we all know that missing 2 hit at the begining of the fight or missing a taunt is really really bad. Expertise because parry gibbs can shoot you but obviously an averaged out fight can't weight that. ArPen was reduced because is the only stats affecting only threat, with boss hitting for less all other aggressive stats increase their TP value except ArPen.
Haste has a negative effect due to increasing parry gibbs and a positive effect due to increasing shield chance. The border line is at 52 expertise. (If you are expertise capped 1 haste = 3 Stam-EQ_TP).

Chocing gear for tanking is not like chocing it for cat. DPS is 1 number and you should maximize it. For tanking & healing the situation is more complicated and more subject to flavor (for example I personally like to gem for stam/exp) that's why I've put TP, DPS, TPS in separate collumns and then suggested my value, but you can build your own starting from them.

Edit: changed 2t8 bonus with the right proc chance (2%).

So, do you hope to gain avoidance, crit and hit from gear, enchants (+agi/stats), food, potions and gem +sta/exp?

someone can tell me how much ArPenRate it is to get the 24%?
and does it mean that ArPen will get one of the best stats with upcoming changes?

15.395 ArPenRating = 1% Armor Penetration (correct me here if wrong, took it from feral numbers)
It seems like ArPen is going to be very strong stat, semiquoting nightcrowler:

So with shred idol, ArPen is the best stat with the gear selection nightcrowler used in his sim.
With rip idol, ArPen is very close to agi.

Keep in mind that the more ArPen you have, the better the stat becomes. So if you have almost none on your gear now, agility is better. 24% is pretty high, I personally have around 11% on my PTR char.

You get to know more if you read night's post, he explains ArPen further in Discussion section. Or you could read Feral numbers thread, where Wulfmanjack posted how good ArPen is with Ulduar loot, and how it gets even better if you gem for ArPen:

Edit: Sorry to Nightcrowler for ruining his name

With Nightcrowler getting himself a rather lengthy temporary ban, I'm not sure what the ETA for the add-on or updates to the current models/simulations will be. I too am anxious to see it in action since most of his information seems to be very good theorycrafting.

If anyone is in contact with him (he has his profile set to not receive e-mails or accept private messages) and could either relay information or post up a location where he is continuing this research and development, it would be greatly appreciated.