I think 4.5T is a lot faster than 10.5T motor.

What you can do to a brushless motor is increase its efficiency like balance
the rotor, install ceramic bearings, have some cooling system, center the
rotor on the stators magnetic field or play around with different diameter
rotor and timing. Also consider the ESC's transistor switching speed since
it is run in electric pulses/frequencies or drive frequencies.

What I dont get is why different motors have different Kv ratings even
though they have the same number of turns. Like Ballistic 10.5T has 4600kv,
but in other 10.5T brand motor, its just rated at 4200kv. I think manufacturers
should include torque ratings as well.