IIRC, the 2 pole rpm limit is +/-150k.....not sure why that number comes to mind, but I don't think you will be ESC limited for rpms on a 2 pole motor(magnet limited, perhaps). :-)
150k - 160k RPM is a fairly safe number to assume for a 2-pole. The real number is based on a wide number of factors and is limited by the ESC keeping timing with the motor.