The Yeah Racing Hackmoto 17T motor, hanging off the rear end of my T4.3, was running roughly 28° cooler than the Reedy motor. At the 10 minute mark, I had readings of 137°F~154°F depending where thermometer was pointed on the motor. The end bell bearing is where I got the hottest readings and the body of the motor is where I got the 137°F reading.
At the 20 minute mark, I was getting 170°-ish end bell readings.
Trying to get traction with T4.3's stock tires and dry/rough track is an everyday occurrence for me in the backyard. I am running 87/16 gearing. Probably could get away with a larger pinion gear if I was only running the truck 10 minute intervals, but I'm very happy with the speeds with the 16T pinion.