For Gorefiend:
1. Try conductivity instead of rushing streams. During the Feast of Souls phase the entire raid is stacked for a long time. That would save you mana since you'll have to cast less healing rains for the same uptime.
2. Raid cooldowns were interleaved nicely, though it seems there was a slight overlap of power:word barrier and your healing tide. It would be nice if power:word barrier can be used when no other raid cooldown are used to cut down on the expensive spell casts while it's up.
3. You can cut down the number of chain heals while raid cooldowns are up (use weakauras to see when they are). For example, when saving mana there is no need to spam chain heal while tranq is up, since the druid tranq is so strong (did 42% overheal on your log), that those chain heals you casted during it are a mana waste since the tranq would have healed the extra damage anyway.
4. During the stomach phase, you used healing surges on the NPCs, which costed you a lot of mana. Use riptide and healing waves instead to save mana, it's OK if you don't heal them to full before they go out, since our spells aren't efficient when they are close to full HP (due to our mastery bonus to low HP). Even if you heal them only to 75%, they will get out with 25% HP, then the DPS can finish them outside.
5. In between the feast of souls phase, there is time to use the channeled draenic mana potion instead of the normal mana potion, that will give back more mana.
For fel lord:
Now that our T17 4-set was nerfed, a style I found to work well there is glyphing chain heal for the 25 yards jump range instead of 12.5, and speccing into echo for the double unleash. In a spread fights, this makes chain heal jump more efficiently, and during the 3 seconds in which we can't cast chain heal, we can use unleash, which will buff the next chain heal by 30%.
This counters some of the theoretical HPS loss of that glyph, and also gives slight mana savings, since it buffs chain heal by 30% but costs 24% of chain heal's mana. In practice depending on the fight glyphing chain heal may not even be a HPS loss, since during those 3 seconds delay if the raid HP goes down (but is still safe from dying), we get higher mastery bonus on the next empowered chain heal.
Also, keep running BRF for the spirit trinkets from blast furnace or blackhand, they are still useful to have for some fights.