Paladin Tanking Holy Damage

Looking at the numbers it seems that 250 Holy Damage is very important for threat. However, you can't ignore your weapon damage either. Your bread and butter is Seal of Righteousness. This takes Main Hand Weapon Speed, Main Hand Top End and Main Hand Bottom End damage into consideration while determining its damage. Unfortunately there aren't any good Paladin Tanking weapons that have both Holy Damage and DPS on them. However, taking a 41DPS weapon with lots of spell damage is a better trade-off, as it allows you to fill your other slots with tanking gear.

Judgement of the Crusader
Judgement of the Crusader is your Main Target judgement of choice. It adds 190 Holy Damage to your total Holy Damage when you have that mob targeted. As well, Light does not return mana from the healing - you want outside healing as much as possible. If you are not able to keep up your threat cycle because you are running out of mana then you might have to keep Wisdom up, but you will be giving up threat generation for mana.

Crushing Immune
Lots of people like to say Warriors are Crushing Immune but that is false. There seems to be a lot of anecdotal evidence that Crushing has been switched to a Proc Per Minute. Mobs have a 15% chance to crush, but most Warriors are saying that as soon as they lose shield block they get crush after crush (which supports PPM). There are no logs to back this up so it could be that humans like to apply patterns where there are none. Regardless - Warriors can be Crush immune for two attacks every 5 seconds under best conditions. That does not make them crush immune.

Now, off Warriors onto Paladins right!? There are two theories about being Crush Immune. Neither have been proven.

 
Your total mitigation (dodge/parry/block) must be greater than 100% to push crushings off. This is the theory supported in this guide. It's believed to be right based off game theory/design (basically the algorithm for 1 roll hit tables supports this theory). This theory means you need to add up your dodge, parry and block together. While the sum of them is greater than 100% you are crush immune.
Your total block percentage must be greater than 100%. This theory says that the only time you are crush immune is when your total block is greater than 100%
 
I mentioned Warrior before because it seems that many Paladins say to themselves, "We don't have the Shield Block ability so we can never be as good as Warriors" (and a lot of Warriors want them to believe that). But Warriors are not Crush Immune - this is even more true if Crushes are indeed PPM. The difference between a base 15% crush vs. a 15% PPM to crush is massive. That means as soon as you become un-immune you will get crushed with near 100% frequency until the PPM requirements are fulfilled.

How to be as crush immune as possible? Get your dodge/parry/block (with specials) above 100%. Then try your best to keep your block rating specials up all the time (harder with Paladins because you can't control redoubt).

Key concept: Block Rating is much more important to Paladins than Warriors.

Crit Immune
As with Warriors, the magic Defense number is 490 to "generally" be crit immune. What does that mean? Blizzard does have the ability to make monsters and bosses have a higher base crit percentage than 5. However, 5% seems to be the default and most mobs/bosses just use the default. However, some mobs (especially the rogue types) have higher than 5%, so 490 will not totally protect you on those mobs. However, like Warriors, it is best to get 490 and then work on other stats rather then sacrifice other stats to get more defense.

TPS Values
A key thing to know about Paldins is their spell-damage co-efficents:

9.2% per 1.0 weapon speed, One-handed Seal of Righteousness 
73% Judgement of Righteousness 
 76% Consecration 
 20% Holy Shield (5% per Block)* 
 9% Avenger's Shield 
 17% Seal of Vengeance (per tick) 
 43% Judgement of Vengeance
This lets you figure out Threat Per Second (TPS) values for each ability.

Seal of Righteousness
SoR Threat  without Judgement of Crusader using a 41DPS weapon.
With 250 Spell Damage it adds 190 Threat with Righteous Fury. By comparison, max-rank Heroic Strike adds 193. If you had 250 Spell Damage and had Judgement of Crusader that would be 257 Threat per attack (or 128 TPS).

Judgement of Righteousness
With 250 Spell Damage it would cause 564 Threat when judged every 8 sec (70TPS). If the target has Judgement of the Crusader it would be 828 Threat. Damage for a decently geared warrior is usually around 400 with Shield Slam, meaning Shield Slam causes about 750 threat for Warriors every 6 sec.

Consecration
Let's look at Total threat for Consecration because it is easier for the math. To figure out per-tick just divide the numbers by 8.

Consecration Threat Graph
At 250 Spell Damage that is 1333 Threat over 8 seconds or 166 Threat per second. On your Main Target (with Judgement of the Crusader) that is 201 Threat per second. For comparison lets look at Sunder Armor. Sunder is 300 Threat every 1.5 seconds if you are spamming it. That works out to be 200 Threat per Second.

Reckoning
Reckoning is hard to determine a Threat per Second value for, as it procs off you being hit. However, we can figure out how much extra threat it generates when it does proc.

Let's assume the same weapon as the Righteousness calculations used. It is 1.8 speed so lets say all 4 Reckoning Charges get used. That means 4 free Righteousnesses over 8 seconds. So, 10% of the time you will generate an extra 790 threat over 8 seconds. (1028 on a Judgement of the Crusader target). This works out to be 98 TPS on non-judged and 128 on judged (SotC) targets. Of course, this only happens sometimes and is hard to count on.