From my experience in the arena, Shadow priests are just too soft for 5s. Theyre always close to the top of my nuke list and are incredibly easy to kill just with the normal CL+LB combo. Dpriest are uber hard to kill. They have so much passive dmg mitigation is ridiculous.

4 SL/SL locks (maybe a full affliction for UA) is extremely stupidly funny. They take an immense amount of damage and become almost unkillable with a healer. with 4x the DoTs its gg. GIven some classes are going to eat through you but with the DoTs up I dont know if theres a way for them to recover. I wont even mention the value of CC.

I have a 3xlock +1x Spriest coming up (lvl62) and a (lvl70) lock on the Spriest account. The more and more I play arena...the close I come to the conclusion that the Spriest will not be needed.

My thoughts...Go for a Hpriest of Dpriest to level up 4 locks. When you run arena get a healer and enjoy the fun, imo I think 4 SL/SL locks is disgustingly OP.