I guess the answer would depend on, doing what? Sustained dps on single targets stationary? Burst DPS on the move most of the time? AOE? Pre-badge horrible gear, badge gear, PvP gear, lfr gear, etc. Are you planning on having dedicated healing?

Not all classes specs do very well at the edges of the single function especially hybrids, which is good for class balance. Some specs are horrible unless they are raid geared. Some specs require specific gear to work almost, some are single stat based almost.

You can easily zone into naxx25, pull a gargoyle and have your a DPS character go at it while your tank keeps it occupied. When it turns to stone back off a few steps into the room that has the portal and set it reset. Rince and repeat until your macro(s) are honed.

You really want to be able to do something more than just DPS a single target, you need to be able to switch targets quickly with very little idle. A lot of proc based spec suffer greatly if they cannot capitalize on their procs. The way the talent trees are currently, this is very key. The specs surround capitalizing on procs.