Leveling at 56-60

I'm a warlock on Laughing Skull, 56 Underpants Gnome.. I just finished off all of my rested experience getting to 56 last night by grinding/running Sunken Temple.. Now I'm at a loss of what to do, since a full ST run only yields 30k xp and takes a couple hours. So I'm asking warlocks or any other cloth classes what did you do from 56-60 to level, or if you know a more efficient way, don't hesitate to share.

Do the onyxia Key quest, BRD, or head to azshara to grind with the farmers

Do Blackrock Depth runs.
This works really well for mages, maybe for warlock too with voidwalker / hellfire / rain of fire --

Go to Diremaul East and do the first pull -- it's about 7-8 non elite plant things that are level 54. Mage can AoE them all down in about 1 mana bar or less depending on how good gear is and how lazy you are with kiting etc. After that pull exit the instance, reset it by invite someone to a group (You can make a macro for this so you invite someone to a group and leave before they accept and that will reset it instantly. Just find someone that's already grouped so you dont spam them with invites) and then do the pull again, rinse repeat. 2 mages I know have got from level 55-60 in about 2.5 IRL days farming DM and have got lots of sellable herbs (AH), a few epics and a lot of nice BoE blue items. I'd be interested in seeing how it works with warlocks.

Have you tried finding somewhere underwater to grind?

That way you can use your underwter breathing and you wont be seen be most people looking to kill you.
For that lvl not sure where right level mobs would be.

ST is a tad low for you now to help you get to 60. My best advice is just to stick it out and grind. In EP there is a spot in the very NE corner by light hopes chapel that is about 20 mobs in and up a hill. You can grind there in pretty much relative piece to 60. Or at least i did from 58 to 60.