If you're running a brushless ESC why not run a lower kV brushless outrunner motor? You'd have more powerband with that low kV brushless motor than you would with a 55T brushed motor.
I run the same HS-645MG in my Axial, you'll love that servo. Tons of torque and not a slow speed at all for the amount of power.
Good luck. I like the chassis design.
