I played PE+EotE.
PE to have a powerful Ele on the boss (who takes increasind dmg), EotE for higher sustained CL-damage.
Not saying this is the perfect setup, but we killed the boss and I came out a close 2nd after our lock.
If you want to Max DPS, you put your Ele on the boss and you pick up Echo...but I thought for "progression/getting through content first" the EM is better than Echo. When you have several Adds our during the Dinomancer burn, that EM + CL combo is incredible burst AoE to shred through targets.