I actually think a power FC offers very little over a Nistune, its really only the hand controller and the nistune actually offers more load points. The Nistune has the added bonus of being cheaper. In a mild build my choice would be nistune, beyond that I would go Wolf, Link, Vipec ect. The power FCs time has come and gone IMO
The stock RB25 AFM will handle up to about 250rwkw worth of airflow. I wouldn't worry about changing AFMs unless you are shooting for something above that.