Another instance I'd like to farm is The Ruined City or Sunken Labyrinth at T2. The final boss drops Morgul Crests if you complete the T2 challenge. These Crests can be used to buy the 5 slot Faramir's Faithful armour.
Faramir's Faithful armour pieces cost 20 crests. The ideal would probably be Pelennor helm and shoulders, and everything else Faramir's Faithful.
My understanding is that you get 5 crests/run divided among 3 players, and it takes about 45 min to run (with practice).
Time per EACH Faramir's Faithful piece (+1 essence slot)
20 crests/(5/3 crests/run) = 12 runs * 45 min/run = 540 min/(60 min/hr) = 9 hours
I also understand there's a way to skip one of the bosses in The Ruined City (used to be able to skip the first two) which could cut down on the time. Let me know if anyone is interested in running this for the crests.