With the significant nerf to 5% on Divine Insight proc rate, the difference between Twist of Fate and Divine Insight is significantly lower - this tier is now reduced to personal choice for the most part. If the fight involves a significant burn phase, then Power Infusion will likely prove the best option. If you can maintain very high uptime, Twist of Fate will prove the highest dps (fights with many small adds or single opponents dying frequently in succession). In multi-dot fights with few execute phases however, Divine Insight will prove best.
Twist of Fate
Twist of Fate increases our damage against targets in execute phase - this is particularly significant because Shadow Word: Death generates Shadow Orbs which translate into Devouring Plagues - meaning our damage during execute ramps up significantly during execute phases. During non-execute phases we generate 3 orbs every 25 seconds, but during an execute phase in MoP we generate 1 additional orb every ~12 seconds, or 2 additional per ~25 seconds, a 66% orb generation rate increase.
In addition, 2 Shadow Word: Deaths replacing the equivalent GCDs of Mind Flays during execute results in another 5,500 DPS increase - so we spike up 15k DPS during the period when Twist of Fate is active! This means that the actual benefit of Twist of Fate may prove higher in practice than it does in the math below, which is already a significant argument in its favour - but lets get to examples!
If you deal 40,000 DPS, and can maintain 100% uptime on Twist of Fate then you gain 6,000 DPS - on a fight where your guild is struggling with the execute phase of a fight, or where you are inundated with small adds - this will prove to be the best option for this tier by far. Even if you can only maintain 33% uptime on Twist of Fate, you are still gaining 2,000 DPS - which makes it better than Divine Insight single target: and that's still ignoring the significant DPS spike shadow sees during execute phase (so it's actually more favourable than it shows!)
Power Infusion will be fantastic for fights with important burn phases, or where a single raid member has a special buff (ie. a mage gains a +100% damage buff that is fight specific). It will also be useful for undergeared Priests to empower their allied Priests (remember: priests before ho's). Conceivably, the 20% haste bonus could be something we will gear around to see additional ticks of Devouring Plague while PI is active. In general however, the benefit of haste is lost on many instant casts such as From Darkness and during execute phases (SW: Death), and therefore Divine Insight is likely to be the superior talent most of the time.
Divine Insight has a 5% proc rate, meaning that without haste on a single target, 20 ticks of Pain will cause 1 DI proc on average per minute, with 20% haste this is a 1.2 proc rate per minute (PPM), with 30% haste this is 1.3 proc rate (PPM). However, the value of the proc is considerable - in addition to the Mind Blast damage itself and the instant GCD that can help you re-position - Mind Blasts generate Shadow Orbs, which result in more Devouring Plagues. With Devouring Plague being such a significant amount of DPS currently, this will make DI the correct choice in some circumstances: Let's Math! ^^
One Mind Blast proc is worth ~48200 damage, one Devouring Plague is worth ~180,000 damage - assuming all orbs are successfully turned into Devouring Plagues over the course of the fight, then each proc of DI is worth one mind blast and one third of a devouring plague, or 108,200 damage per proc. At a proc rate of 1.2 per minute on a single target, this means DI is worth 129,840 damage per minute: 2164 DPS per target. So if you can maintain DI on 3 targets, then it's 6492 DPS.