Ever hear of Sunwell trash farming group? google it.

You dont need to be in t6 to farm this shit.
All you need it is minimum 5 mages, 1-2 good t4-t5 tank, good aoe healers.
DPS doesnt really matter. You can do this with 12-15 ppl.

Have a hunter MD the 1st pack AVOIDING the Sunblade Protector. (The protector cast chain lightning non stop for 4k, impossible to take down in a small raid)
Sheep all targets and except 1 (healer) and burn it 1 by 1 while keeping the rest sheeped. Loot it.
Proceed with 2nd pack. Repeat the same thing and loot it.

Run out, disband raid, switch another raid leader and reform raid.
Rinse and repeat.

My server does this Pug all the time to farm new leet patterns, epics, sunmotes and gems.
Ya. Shivering Felspine drops like candy too. In fact, it drop twice in one run last 2 weeks ago.

Its not that hard.

Note: Its important to kill the 2nd pack coz it contains a different variety of mobs including Archmage.
The Archmage likes to drops stuff from what i have observed.