Deactivated1240/Power Levels

Is the power levels of the Charmed Ones equal, or are they different, getting lower with each sister? We all know Prue is the most powerful because she's the oldest, but it seems that she, if she had lived, would be more powerful than Piper, and Piper is more powerful than Phoebe, and Phoebe is more powerful than Paige because of her new Empathy advancement. So how does that whole power thing work?