Yep I'm doing 1x priest 4x warlock also - I thought about 5x warlock but the priest opens up so many more doors for you - plus I think the damage will actually be higher with a shadow priest, with shadow weaving, etc, plus better mana efficiency.

Also if you decide you want a good healer later you can always just respec the priest holy, or discipline for a really good pvper.

Anyway, priest gives you way more possibilities and still meshes quite well with 4x warlocks