The trend for monks in Inferno so far is not to stack HP like the barbarian, but to stack their resists as high as humanly possible.
As a result of this, it’s not uncommon to see more and more monks wandering around inferno with just 20k-25k HP, like their wizardly counterparts, and do just fine.
The reason for this is that their effective health is miles ahead of their flat health.
Stacking resists and armor has the effect of reducing the amount of damage you take based off of a percentage amount instead of a flat amount. This means that the bigger the hits that are coming in, the more work that the percentage reduction is doing for you.
If you stack up enough armor or physical resist to reduce physical damage by 50%, you’ll block the same portion of damage whether you take a hit for 100 or 100000 (half of it) but that 50% means a lot more to the 100k hit than it does for the 100 hit.
In inferno mode, with the mobs hitting for some ridiculous numbers, that percentage reduction becomes the best way you have of reducing the damage you take. Flat health increases will help only as much as you have enough percentage mitigation to back it up.
The thing about percentage mitigation though, is that it’s exponentially effective. It becomes more and more effective the closer you get to 100%.
To give you an example, let’s say that there’s a monster that will hit you for 1000 damage and you’re sitting at 50% total damage mitigation. The result would be that you take 500 damage total.
Now imagine that you stack up enough gear to gain an additional 2% mitigation, bumping you up to 52%. That same monster hitting you for 1000 will now deal 480 damage instead.
That’s not that much difference right? At the end of the day, 2% will only save you from taking 4% of the damage.
Now let’s head up to the higher mitigation numbers and see how that dynamic changes.
With the monster hitting you for 1000 again, let’s say that you had 96% total mitigation. You would take a total of 40 damage.
Now again, let’s pretend that we manage to stack up enough gear to go up another mere 2% mitigation, bumping us up to 98% total mitigation. The same monster hitting us for 1000 now only deals 20 damage to us.
All of a sudden, that 2% seems huge. The same 2% increase in mitigation went from reducing the total damage you took by 4% (500 > 480) to a whole 50% reduction in total damage you take (40 > 20)!
The important thing to take away from all of these numbers is that the same amount of mitigation does not always result in the same amount of damage reduced. The more reduction you have, the more effective every further point of reduction becomes so consider that when you’re sitting at 95% and you’re trying to decide between another 4000 life, or another 2% total reduction.