Hey Trubo, the amount of haste you need to get 3 extra ticks out of Rejuvenation under SotF (which is what I assumed you'd have in all my calculations over in the article we're discussing) is 1345 so long as you have a source of 5% haste in your raid (e.g. shadow priest, boomkin, ele shaman). I'd imagine most Resto Druids who are raiding already have that much haste.
To get yet another tick it'd take 8080 haste or thereabouts, which I reckon is not worth giving up the Mastery for. I mean, on normal mode, each tick of Bathed-in-Light-boosted Rejuv will tick for around 100k, so getting that one additonal tick on each breath is only like 300k healing, and it's easy to see how dropping a lot of Mastery would result in losing more than 300k healing over the course of all your spells.
One thing I should do is figure out whether it's worth it to add WM:Bloom in since I believe the detonation is off the GCD. I really need to go back and revise some of my strategies now that I've got a better understanding of how the fight works on Heroic mode anyway
~Dayani@Healiocentric