You forgot 10% crit block through HtL so ~50 mastery is sufficient for reaching 85% crit block chance (which seems to be enough to be crit block capped). It is not possible to permanently reach this mastery level and even if you try to get close (40+) you will have only 200k HP or less so it's not that viable.

Its either 2 or 3 of your examples, though its hard to tell currently because you would need to be well past the block cap to accurately test it since the results would end up the same before that. I want to say someone over at Tankspot did the testing to prove it but its been awhile since I saw the post.

From what I've seen on this forum, it's probably safe to recommend, stack Mastery until CTC without using Mastery trinkets or the Mastery elixir. If you haven't done so, then start matching socket bonuses. After that there are at least 3 different views. In order of popularity here I think, we have:
1) Stamina
2) Dodge and Parry
3) More Mastery - Provides only more Critical Block past CTC, but arguably still powerful.
I suppose it depends on your raid team. Stamina will work fine, if you have the healers to pour on the heals. Dodge and Parry provide the best reduction in average damage taken, but is perhaps most spiky answer, giving your healers the most RNG to contend with. More Mastery converts some normal blocks into Critical blocks, but Mastery past CTC is perhaps the least understood thing here. I am guessing that more Dodge and Parry does push Critical blocks. Perhaps like this: An increased 1% Dodge forces more normal blocks to be Critical Blocks, as excess block converts to Critical block. The 1% Dodge pushes you deeper into Critical blocks. More Critical blocks. That would seem to be the physical damage answer, while Stamina is the magic damage answer. Perhaps shading between the 2, Stamina and Avoidance, depending on your current threshold boss and your raid team make up will serve you well.

As a general rule, considering how much magical/unavoidable physical damage there is in Dragon Soul, stamina is really the way to go once you're block capped. The only fight where extra avoidance would be on par is heroic Blackhorn, and even then, I'd prefer the stamina to help with the stacking DoT in phase 1 as well as the shouts in phase 2.

The last option, which I hesitate to bring up, is to stack threat stats (hit/expertise) past the block cap. This will help your raid with meeting some of the strict enrage timers in Dragon Soul, but since a lot of the tank damage you'll encounter is still pretty dangerous, I would just stick with stamina.

I also believe it is a 2 roll system, but it's often good to check our assumptions.

I think it's all on the same roll though. What I mean is the CTC table knows exactly how much is supposed to be blocks, and your crit block% replaces your blocks, but only as a percentage of the blocks on the table. So if you have 70% block and 50% crit block, you end up with 35% blocks and 35% crit blocks on the table.

The way to test reality would require 30% (or more) avoidance from dodge/parry and another 80% block chance, just to get a good sample percentage. My stats aren't high enough to test yet, so hopefully someone with great gear could put in some time. You turn your back to a player, just to see what a basic white hit does, then you face the player and start blocking, say 1000 attacks. Try to get a tally of hits that are blocked and those that are crit blocked. Then you change the table by doing the same thing with shield block up. If the change in crit block % is exactly what the SB tooltip says, it's method 3), if the change is much smaller, we are likely looking at 2).

I'm not sure this is the correct way of testing 2) vs 3), since what I've heard with shield block up also passively overcapped CTC (or any temporary ctc buffs you have present when shield block is on) gets added in to the crit block chance, as in shield block increases your crit block chance by 25%+overcapped percentage, making you get full benefit from overcapped mastery for the duration of the Shield block.

I could be wrong about this though, but at least the Shield Block buff tooltip reflects this behaviour. So, if you wanted to test how it works with un-shieldblocked, over cap mastery, you'd have to have a very large highly overcapped mastery, with a mastery proc trinket for example, and then test out how many crit blocks you're getting with, say 100% block 15% parry 15% dodge 5% miss VS 70%block 15%parry 15% dodge 5%miss.

If I understood what you were going for here, in the first scenario you should be crit blocking every time the mob hits you, as you should have 80% or so crit block, and with 100% block the combat table would look like 80% crit block 15% parry 15% dodge 5% miss with some crit block pushed off the table. In a two-roll system however around 13% should be normal blocks, 35% avoided and rest crit blocks, or with 100% hold the line uptime, 6.5% normal blocks.

With the mastery+stamina proc trinket this could probably be tested.

I was thinking some more on the what to do after reaching CTC question? Mastery versus Dodge and Parry at CTC. What if at that point, we traded Dodge and Parry for more Mastery, staying at CTC? We would get more normal and critical blocks and less Dodges and Parries.

To reduce Mastery, and add Dodge and Parries, lowers our critical block chance. I think the best part of block, is a high average block.

This more Mastery approach, would seem to stay on the same path we all took on the way to CTC, for similar reasons, without pushing past the Mastery DR point. Perhaps to continue eating more cake.

What you seem to be asking is whether we should turn 0% hits into 38% hits. To that I would say no.

If we are gearing for survival, stamina is still the best stat. If we gear for mitigation, dodge/parry and mastery are about the same. Dodge/parry gives slightly less damage, but more spike damage. Mastery gives less spikey damage, but more overall damage.

Since we cannot reforge into stamina, we gem for it while maintaining CTC, then we go for CTC with mastery. If we instead put in dodge/parry gems, we would have trouble hitting CTC until nearly BiS gear. If we put in mastery gems past the CTC cap, we are wasting a lot of mastery's benefit, but what we gain is about equal to what dodge/parry give after DR.

Its a two roll.

And avoidance is better than mastery at smoothing dmg intake past CTC. Opposite of "more spikey".

We are unsure if its a 1 roll (the percent based he described) or 2 roll system because the results would be the same before the CTC cap. But its a bit easier to test than people are making it out to be. There is a CTC level where you would be crit block capped with method 3 when shield block is active but would not be under method 2. Then you just need to gather the all the data while shield block is active and look for a non crit block. Youd probably need a sample of 600-1000 hits to be certain.

It rolls combat table. If blocked, it rolls crit. If you have 60% block and 25% crit, you have 45% chance to normal block and 15% chance to crit block. I don't understand which part you find confusing.

Why, because "18>10"? Thats meaningless. There is a good article on TS explaining how best to approach this called "Power of Avoidance" IIRC.