I'm no maths wiz, but figured I may as well have a go... Proc'ing my JC trinket (yes, I have crappy gear :p) which gives +1425 STR my paperdoll parry rating went from 1231 to 1588, which gives a STR -> Parry Rating conversion of around 0.25. I also removed some STR and the rating changed more or less in line with this value, so I think it's accurate.

So the 60 STR from the enchant would give 15 Parry Rating. This is where my maths probably gets a bit flaky though ... Before DR it looks to me like 1% parry is roughly 85.5 Parry Rating. so 15 PR would be approx. 0.175% Parry. Taking your numbers from before:

Str/Mastery: 0.13% Damage reduce + 180 AP + 0.175% Parry (before DR)
Stam/Dodge: ~1250 HP + 125 AP + 0.20% dodge (before DR)

I *think* that would put the Str/Mastery enchant slightly ahead on mitigation, so while shooting for 102.4% it would have the edge.

Yes, I posted before the blue post updated us on Vengeance, so my numbers will be wrong.

Just did a little fiddling with stat weights, it looks like if you absolutely stack the crap out of a stat (easier to do with Dodge because AGIL affects it more than STR affects Parry) you can get high enough totals such that DR drives the value down to roughly 0.85 of Mastery. Alternatively, if you avoid a stat like the plague, you can get it its value up to about 0.95 of Mastery (my earlier numbers on Parry were too high because I wasn't incorporating STR at all). Which gives us a decent range.

So, updated numbers:

Weights
Mastery 1.00
Parry 0.85-0.95 (depending on DR, the more you have, the worse it is)
Dodge 0.85-0.95 (depending on DR, the more you have, the worse it is)
Armor 0.56
AGIL 0.51-0.57 (60% of Dodge)
STR 0.43-0.48 (50% of Parry)

One surprising finding was that extreme levels of Dodge or Parry don't seem to move the DR needle as much as I expected. Keeping Dodge and Mastery at current levels (1127 + 1184 AGIL and 2606 Mastery, respectively) but increasing Parry + 0.5*STR to 4000 only decreases damage reduced per 10 itemization points of Parry from 0.0959% to 0.0842%. BUT, it increases the value of each 10 itemization points of Mastery from 0.101% to 0.145%!

Obviously, if you had both Dodge and Parry at 4k, Mastery's value would be negative because you'd be long since unhittable, so this math will start getting funky.

Perhaps this is the explanation. The value of Mastery rapidly climbs once you start getting close to unhittable, and I suspect Dodge and Parry would as well, except that they're being held in check by DR.

Given the proposed ability to train Rebuke rather than having it as a Ret only skill, has anyone else started thinking more about a hit set? Perhaps this is biased toward 10 man's, but if I'm going to be in charge of interupting something reliabily, I should probably see to it that my interupt doesn't miss. As of right now, I simply don't tank those mobs that would require faster interupts because of the GCD constrained nature of HOJ and AS (it's just easier for our warrior tank to take that mob). The problem is that I've been reforging/avoiding hit since threat is such a non-issue so once we get Rebuke, it's not going to be reliable. At present, I've simply made a 2nd set of gear that gets me within .5% of hit cap, but sacrifices around 5% mitigation to do it. Any other 10 man tanks have any thoughts on the reliability of our interupts versus the drop in mitigation we'd need to get it? I'm going straight mitigation and swapping out to hit for fights where I'll need to interupt (Water Guy on Ascendent Council, or Tron Council come to mind).

I did some experimenting with gems on my Tank Pally.

If your goal is Mitigation and reaching the cap, I would remove all Yellow and Blue gem sockets using Regal Dream Emerald (Dodge/Stamina) and Defender's Demonseye (Parry/Stamina) and replace them with Puissant Dream Emerald (Mastery/Stamina). It qualifies as Yellow and Blue for socket bonus.

The net gain for Combat Table Coverage (102.4%) on my toon was about 1.10% by doing this in all sockets.

This seems so obvious that we should consider removing Regal Dream Emerald from the field manual.
Since it is also Blue/Yellow, just like Puissant Dream Emerald, there is not any scenario where it would make sense to choose Regal.

The only possible reason to consider Defender's Demonseye is if you have a Red gem socket.

At a minimum, perhaps the list of gems should have a (recommended) tag with an * explaining the reasons, similar to the Glyphs section.
This could be a good aid for new Pally tanks figuring out how to optimize their gems and sockets.

The only time you would want to use Regal over Puissant is if you are at or over 102.4 cap and want to convert some block into dodge.

Or if you're tanking Halfus and he's got his MS buff going.

Remember, there are always exceptions. Its not a good idea to be too dogmatic.

Seems like some people are missing at least some of the point of the gemming rules.

If you want to max out mitigation AND match the socket bonus, then you fill a yellow socket with mastery, a blue with mastery/sta and a red with mastery/parry.
If you don't care about the socket bonus, then you'd just pick a mastery gem.

You can't just interchange the parry/dodge combination gems with mastery since dodge/parry is red, mastery is yellow.

It's also my understanding (but I could be wrong here) that once you do get to 102.4, your next best "go to" for enchanting/gemming is to get more stamina while staying at 102.4 and not convert blocks into dodge/parry. You can't always do that because sometimes the socket bonusses are too nice to pass over, or some enchanting slots don't come in Sta varieties. So converting some block to dodge/parry will happen. Adjust your mastery from gems to more stamina if that happens.
Converting block to dodge is usefull, but once you are at block cap, more stamina is a better way to stay alive than block to avoidance conversion, or am I missing part of the point of the manual?


edit: changed 'avoidance' to 'mitigation' to be in line with thecks comment further down.

The new fish feasts, goblin barbecues, and dragon feasts all give a dodge bonus when well fed. It might be a good idea to keep a stack or two of parry food in your bags in case your dodge % is much higher than you parry %.

I deliberately stay away from making specific recommendations in this regard because with how content is now and the philosophy that Blizzard has stated with this expansion one gemming/gearing method may be applicable to one raid tier but not another. Additionally, depending on how your raid is composed impacts what you should to do. Stamina stacking after 102.4% is equally viable as mastery/dodge/parry swapping. It all depends on the context.

That would be pretty counter-intuitive, since mastery doesn't give avoidance.

These terms have had well-established definitions since classic, let's be a bit less careless with them. This is EJ, after all, not the battle.net forums.

Avoidance - prevents 100% of damage from a single attack - Dodge, Parry, Miss
Mitigation - prevents a portion of damage from an attack - Block, Armor, Resistance

Block is not avoidance. If you want to talk about total Avoidance+Block in regards to reaching 102.4%, Combat Table Coverage (CTC) is a far more accurate term, as well as being less ambiguous.