The bbshd can handle 4000w for short term acceleration. Continuous at 4000 will fry the motor. I have one on EBay with a modded controller if you're interested. Firmware on the stock and modded controller upgraded to allow for customization.
Once you add the hub motor you will barely use the mid drive. I have a bafang 750w mid drive and a 3000w rear hub from nbpower. The rear hub is so responsive that I barely use the bafang anymore. I use the bafang for a backup system and to run my headlights. Once you get the hub motor installed...
Mine peaked at a little over 1400w on 52v or 28 amps. Pushing it much higher will certainly fry the stator. I cooked my bbshd at 4000w at 52v. The magnets came out of the rotor.