for leveling up 'till outlands at least, speccing the 4 locks for hellfire (17 in destro i think?) and the priest for AoE healing makes SM / ulda / ZF go by real fast. 4 voids out, 4x hellfire going with priest spamming group heal will pump out an amazing amount of dps for your level. You can send out the void walkers to different targets then /petfollow them back to you for nice riskfree AoE pulling.

If you are more into the quest grinding, I think affliction for the locks and shadow on the priest is probably just fine.