According to datamining carried out by MMO-champion, the tanking trinket available in Icecrown 10 man (normal mode) will have the following effect:
Each time you dodge an attack, you gain 24 stamina for the next 10 sec, stacking up to 10 times.
There is no indication as to whether this is an on use effect, whether there is an internal cooldown, or whether it is simply "always on". I doubt it is an on use or internal cooldown effect, since there is no length of time listed for the buff. I presume therefore it is always on.
The trinket would therefore be 240 stamina, but it would take quite a long time to warm up.
Dodgy maths incoming...
Suppose your dodge chance is d.
Then the expected number of melee swings before you dodge an attack is 1/d. This means that if you ignore the possibility of the buff dropping off due to going 10 seconds without a dodge, the expected number of melee swings before you dodge 10 attacks and you have a full stack of the buff is 10/d. For example, if your dodge chance is 24% you would expect to receive 41.67 swings before the buff stacked to full.
Bear in mind that a 5 minute fight is 300 seconds, so with a boss swing timer of 2.4 seconds you will receive 125 swings in the whole fight, meaning that the full buff will only be up for (125-41.67)/125 = 67% of the fight.
Now, we also need to consider the possibility of the buff dropping off, perhaps due to encounter mechanics (eg the boss ceases attacking, for whatever reason, or there's a tank swap). For Northrend Beasts / Gormok, for instance, this trinket would be useless because the buff will just drop off when the other tank is taking impales. In normal combat the probability of the buff dropping off just from a series of melee swings failing to be dodged is actually pretty high - in ten seconds you will probably be attacked 4 or 5 times, meaning the probability of the buff falling off is (1-d)^4 or (1-d)^5, ie 25% or 33% where d=24%.
Running with this example - given that it will take you 41.67 melee swings on average to get the buff to full, with 2.4 seconds between boss melee swings you are looking at around 100 seconds and in each 10 second period there is a 25%-33% chance that the buff falls off. The chance of the buff falling off in that 100 second period is very very high - I put it at above 95%. This means that the chance of the buff ever topping out at +240 stamina is pretty small, and means that unless there is a large stat buff as well as this effect on the trinket, the trinket will go the way of the ToC10 trinket in being a useless piece of junk.
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