Might be lower than you think. Take a look at your shield block BUFF next time you pop it.

My understanding is that Critical Block is a 2nd roll that happens when you successfully block.

What is the reason for not tanking with a fast weapon? I thought a faster weapon would simply mean more Heroic strikes/ Cleaves. I didn't realize there was any downside.

This used to be the case when heroic strike was a spammable, on-next-hit attack.

Now it has a cooldown.

Okey wanted to get another opinion on my math, this is regarding the +2%armor meta VS. the +5%block. I didn't know if critical block is affected by the meta but i assume it is (corret me if im wrong). Heres what i got, again correct me if i'm wrong.

The 2% Armor meta is (with my gear)+704 armor or .48% armor gain.
Now the Block Meta gives me +1% dmg reduction on block.

Now lets simulate these numbers, lets say we are fighting a boss that hits on average for 40k, and hit me on average 300 times in a fight. The Armor meta will mitaged roughly 196 dmg extra a hit, and over the corse of the 300 hits 58,800 dmg.

Now lets take are block, and this is where the math gets iffy because there are alot of variables for my napkin math. but lets continue with the same idea. Average hit from boss is 40k and we are talking 300 hits. my block atm is 52.64% this means i should block 157.92 hits (158). at 31% block reduction on a 40k hit = 12,400 reduced. at 30% block reduction on a 40k hit=12,000 reduced (400 difference). now we take 400 multiply it by 158 and we get 63,200 extra reduced dmg from the meta. thats 4,400 more dmg reduction than the armor meta takeing a 40k hit 300 times. i may have missed a varible along the way, if so feel free to fix my math but i'm confident that i have nailed it on the head. take it away EJ forums!

If the 2% armor class bonus increases your armor class from 58.14% to 58.72% (I think that is what you are describing), it doesn't mitigate .48% of the 40k hit you're taking with 58.14% armor class, but .48% of the ~100k hit you would be taking with zero armor class.
Another thing you didn't include is critical block. You are currently at around 12% critical block, which would increase the Eternal Diamond's score to ~70.8k.
Edit: Note that all our calculations are without Shield Block or Hold the Line.

Hmm, it would appear that Shield Block always doubles your Critical Block chance. I've changed some items around and checked the buff and it was always showing an increased Critblock chance equal to the amount of Critblock that I already had.
This is however also the first time I hear about Shield Block doing that, was there any information on this previously that I just missed or is this a fairly new find?

In any case, this makes Shield Block a fairly significant cooldown - it is very real to reach 100% Critblock with Shield Block up before even reaching the "normal" Block Softcap, which makes Shield Block a 60% reduction on melee hits on a 30 second cooldown at that point, which is pretty damn good.

Mastery provides comparable damage reduction to dodge and parry going from 100% melees to 70% melees. Going from a 70% melee to a 40% is more damage reduction. Meaning, Mastery is better at reducing damage after unhittable than it was before. Especially since you will be higher up the DR curves on your avoidance stats.

There is no "theoretical point" where we switch back to dodge and parry. If you hit 100% critical block - sure, okay. If you can hit unhittable passively, you'd be ~35% passive critical block. And then when you hit shield block you'd be up another 50% bringing you to ~85% crit block before hold the line. Essentially: when you hit unhittable, shield block will almost bring you to crit block cap.

The question then is: If you can hit 50% passive crit block is it worth it to keep pushing mastery as you push shield block off the combat table. And keep in mind this is all dependent on bosses not catching expertise in later tiers (though this would be independent of block)

So if you are at "Soft Critical Block Cap" then shield block naturally brings you to crit block 1/3rd of the time. And since the mastery argument is always centric in damage reduction comparisons to avoidance... Meaning: independent of "smoothing out the damage" - no I'm not an advocate, but it gives them a leg up stepping into the argument.

Mastery brings your critical block up twice as fast as it does pre unhittable, because the block portion is also converted to critical block. So stepping from a a 70% melee to a 40% melee is a 42.8% damage reduction.

179.28 mastery rating would bring you 3% critical block.
176.71899 dodge would bring you 1% pre dr avoid.

The rest of this will be laid out relatively. Meaning that if you are at 30% avoidance, 1% avoidance is ~1.4% damage reduction, not 1% damage reduction. But since you are at equal levels of avoidance given the argument, the mastery/avoidance argument has the same reference point. If you want, you can bounce the numbers through, but the conclusion should be the same). Just thought I'd mention this in case I am missing a glaring issue where it isn't.

Moving on,
1% pre DR avoid is 1% damage reduction all the time (independent of shield block - pre DR)
3% critical block is 1.28% damage reduction (before shield block), which only works 2/3rds of the time (thanks shield block) and is therefore only worth 0.85% damage reduction on average.

So where does avoidance DR to under 85% efficiency?
Around 1000 avoidance rating. (Nice greens)

TLDR
Until you hit 100% passive Critical Block, mastery will still warrant more damage reduction than avoidance.

EDIT:
Thought I would include this for the sake of elegance:
Imagine the last 3% of hits that you are trying to cover with avoidance or mastery after unhittable.

Normal Block (baseline)
70 + 70 + 70 = 210

~175 avoidance rating (assuming no DR - lawl)
70 + 70 + 0 = 140

~175 mastery rating
40 + 40 + 40 = 120

I don't understand why Impending Victory shoulnd be skilled for something like cruelty or deep wounds. The last 20% of a boss mostly is the hot phase, where healers are going to be oom. It's the time my rotation changes into devastate, devastate, victory rush and so on.

Hi, why do I see lots of tanks with around 1% hit ? :X Should I reforge all hit into avoid or hold hit cap cause of aggro and important things like interrupts? thx and it's for 10 men raids

The only strong reason to gear hit is so that your interrupt doesn't miss. It does of course provide a bit of a threat boost, but in most cases that won't be a big issue. Basically, if you have to take a piece with some offensive stat on it, there's a strong argument for preferring Hit above all else (Expertise being the other strong choice, will do add more damage and threat, but doesn't help with interrupts).

As long as you are able to hold aggro, it doesn't make sense to give up mitigation stats for more offense. The tank's entire purpose is to mitigate damage.