Depends on attack speed and DPS.
at 10k DPS Life Steal isn't going to be very effective.
at 1 APS with a 2 hander life on hit isn't going to be very effective.
In general, monks tend to perform ~6x their paper doll dps using the cyclone build with a decent amount of crit chance. Lets round down to ~5x. Lifesteal is 20% of stated value in inferno, so lets say you get ~1% lifesteal (5% of 6% max).
At 100k dps, 5% lifesteal will get you ~100k * 5 for real dps = 500k dps * 1% = 5k healing per second.
If you have ~2 attacks per second and use thunderclap (1.5 APS modifier + 0.75 proc rate) you get ~3 attacks per second getting 0.75 of your life on hit amount, for roughly 2.25x your LoH total. That means you need ~ 2222 LoH to equal ~ 5% Lifesteal.
Keep in mind that Life on Hit will be a far more consistent healing value that works on things like mobs that are shielding, where as Life Steal will be far more effective when aoeing mobs.
~ max LoH values:
Rings (x2): 450
Weapons: 950 x2 for 1 handers, or ~1900 for 2 handers (same total)
Thats ~ 4k max LoH, hitting 5.2k with life on hit gems.
Lifesteal caps out at 6% hard value.
LpSS RULES SUPREME!
As for what the above poster was talking about, i was able to tank uber bosses at MP7 with nothing else than LpSS.
The best thing to do IMO would be to get as much LpS on your armor gears as possible, get a 50+ LpSS Inna's Radiance and then to get 2 fist weapons and make sure both of them has LpSS and one of them has 3% LS.
With that set-up you'd have more sustain than you'll ever need.
NB: LpSS set-ups only work when you're using FoT: Quickening or have a high spirit-regen build. Obviously, you've gotta be generating enough spirit to spend it all the time into heals.
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