I have made some alterations to my gear and have decided to drop teh 4-piece bonus in favour of better gear. I have switched up some of my talents.
Cascade -> Divine Star / Halo
Power Infusion -> Twist of Faith
I use PW:Solace, PoM and PW:S (rapture) essentialy on CD constantly; I have addons that ensure I don't leave it off cd for too long.
To my suprise I didnt really have mana issues as bad as I thought I would have. I have started to atonement heal a lot more but it seems to even out, the damage is there (about 70k dps when I'm really focusing on atonement) which of course translates into better healing.
I'm kind of nervous about pulling the trigger and going full crit. Right now I'm at about 23 percent crit chance while I've seen some people who are only about 3-5 ilvls bigger than me with crit chance up to 30 percent. I dont know how you can achieve these numbers without sacrificing something significant.
I've only done ToT LFR though (legendary quest farm) so I will have to see how this will translate into flex (having trouble getting into normal raids atm).
Now - about mana. A game-changer for me was the MINDBENDER - 30-50k mana return every MINUTE! Combined with selective shields (free when used up) and trinket use - I'm rarely mana starved and find the extra output by min maxing crit and mastery over spirit is providing more healing and absorbs and thus needing fewer casts and maximising heal per mana that way.
Hope this helps.
I'm actually really surprised about you not having any mana issues. You have 7.5k spirit UB, which to me seems shockingly low. I'm trying to reforge spirit to some more crit myself but am extremely antsy about something like that.