When I was on the Interclub committee I took the responsibility for arrangeing the testing of the 4300 for suitability to be included in 19t.
I purchased a motor and had both Anthony and Scott do some test.
At the end of the tests Anthony's summation was "I would have no problem racing against a 4300 with standard rotor with a 19t brushed" - from my observations of the races where it was used by Anthony, Scott and others, I agreed.
On that basis I recommended to the Interclub committee that the motor be included in the 19t class.
I expect that the committee will make a formal statement in due course.