Go with brushless at my local track we start running both brushed/brushless at the same class, 4300(19T) Class and 13.5(stock) class. I've run my GTB/4300 for the first time out and won the 19T expert class. After 6 years of racing I'm done with brushed motor.
Gearing brushless motor is different from brushed motor. You have to gear brushless too the moon to get the top end of a brushed motor if your running touring car FDR = 5.5 or lower
Brushless motor has more torque than a brushed so you have the advantage on the infield or tight tecnical track. Brushless motor is a rocket coming off corners.
It's true with a Novak GTB speedo there is a chance you will thermal but it can be avoided. You gear the motor based on ESC temp, keep it below 170 degree and you will be fine. And also upgrade to sintered rotor, and large front endbell this is necessary to able gear the motor lower without thermalling.
All I can say I'm very pleased with brushless system, peformance never fades it's always there when you need it. It's like having a new tuned motor everytime you put your car on the track. You can play more with setup of your car and improving your driving skills rather than dealing/tuning your motor everytime to be competitive.