First of all consider that the formula for shield damage reduction is given by:
X = SBV + STR/20 - 1
So if you would have been hit for 200 had the attack not been blocked, you will be hit by 200 - X
But, you probably have Shield Specialization, so the formula is really
X = 1.3*SBV + STR/20 - 1
So each point of SBV actually blocks 1.3 damage.
So now let's take a look at the trinket. Every time you block X is increased by 59*1.3 if it's not active, and 259*1.3 if it's active. Assuming full up-time this means that 17% of the time you're blocking 336.7 additional damage, and 83% of the time you're blocking an additional 76.7 damage. Over time this averages out to (.17)(336.7) + (.83)(76.7) = 57.239 + 63.661 = 121 damage.
So, every single time you block, you block an additional 121 damage than if you were using something else. That's not just a little damage mitigation, that's A LOT of damage mitigation.
The good thing about SBV is that it doesn't suffer from diminishing returns, and especially if you're using Shield Block often, you will block a ton of damage.
And none of the above even begins to factor in the additional threat you get from Shield Slam with the auto-blocker.
As you can see SBV increases your
Effective Health by more as the mob hits for less. And SBV increases your Effective Health by less as the mob hits you for more. This is because SBV reduces damage only when you block, and by a fixed amount. So let's say you have 20,000 effective health (a function of armor and hit points, and excluding SBV) and the mob hits for 5,000 raw damage per hit, and because of your SBV you block 500 damage per hit. The mob will have to hit you 5 times until you die. Therefore SBV blocked 2,500 damage total, therefore your effective health including SBV was actually 22,500.
On the other hand, let's say the mob hits you for 2,000 raw damage per hit. The mob will have to hit you 14 times to kill you, thus you blocked a total of 7,000, thus your Effective Health was 27,000.
Moral of the story is, on mobs which hit extremely hard, maybe you would prefer Stamina. But on mobs which hit for more reasonable amounts you might prefer SBV.
In fact, this leads me to wonder if the relationship between SBV and Effective Health can be quantified precisely with a differential equation, and thus solved for an exact formula.
Edited, Jan 8th 2008 4:56pm by duvar