what pinion for brushless blaze

[mikepro4]

Dear All

Have obtained a reedy 6100kv brushless combo for my blaze, but can't find any info on what pinion to fit.
she's running the kit 45 tooth spur.
The standard motor that came with the car can run 11-22 teeth , i already have tried her with a 16 and 13 and in both cases the motor runs very hot,not think the thermo cut out came in but, have been told that when running brushless you should go down 2 teeth from the standard motor, so should have thought both the ones tried should have been ok.
can anyone give me an idea of what i should start with?
regards
mike