It's official! Castle have lost the plot (in a good way)

[SpEEdyBL]

This motor on 2s will not be any faster than than a cms 5700 motor on 3s.

9,000 x 7.4 = 66,600 rpm
5,700 x 11.1 = 63,270 rpm

And if you take into acount that the 5700 setup will be slightly more efficient than the 9,000 kv setup, you will be able to gear the 5700 up to match the rpm at the wheels. Not only that, but the esc will create more than twice as much heat with the 9000 kv setup.

So no need for there to be anything special for the rotor or bearings compared to the current existing motors.