So I did some math, which you can view below. The point was simple: figure out if farming Torments over Normal-Master difficulty is worth it. Turns out that it's really not, unless of course you can clear the Torment in a specific amount of time in relation to a lower difficulty.
So stop farming Torments because you want to show off your giant ego, or your sheet dps that honestly doesn't mean anything. Instead, save your time and take a look at the table below.
|Difficulty||Legendary Drop Rate||Rift Legendary Drop Rate||Time (in minutes) to Complete (Rifts)|
|T1||1.15||1.44||1.15 (30) = 34.3|
|T2||1.32||1.65||1.32 (30) = 39.6|
|T3||1.52||1.9||1.52 (30) = 45.6|
|T4||1.75||2.19||1.75 (30) = 52.6|
|T5||2.01||2.51||2.01 (30) = 60.2|
|T6||2.31||2.89||2.31 (30) = 69.4|
|30 minutes is just a base. You can substitute any number in there. The key isn't the time, it's the ratio. Rift Legendary Drop Rate of any Torment/Rift Legendary Drop Rate of Normal-Master * (time it takes to complete normal-master). For example, T1 @ 1.44/Master @1.25 = 1.15 (30 minutes) = 34.3 minutes to make it worth your time.|
If you want an exact number for yourself, run through a Rift on Normal, Hard, Expert, and Master. Record this time and use the ratio from above to figure out exactly the time you need to complete it. If you were to complete Master in 16 minutes, you'd have to complete T1 in 18.4 minutes. Taking you 42 minutes? T1 needs to be done in 48.3 minutes.
It's that easy! Now get grinding!
If you notice something wrong with this table, please let me know. I'd love to discuss this as it's been driving me crazy ever since I started playing Diablo 3. I realize that Torments offer better gear (at a very low rate mind you), so I'm not saying that you shouldn't farm them. I'm simply saying that until you can one shot most enemies in a specific difficulty that it's not worth moving up.
You aren't strong enough to complete it in a fast enough time to make it worth your while.