I don't think you're going to lose torque by going up one tooth on the pinion. Reason being brushless ESCs have Punch settings. In other words if you gear up and find that you lose punch/torque all you need to do is increase the punch level.
Most people have the misconception that brushless motors behave like brushed motors when they really don't. Brushed motors have limited torque no matter how much current you feed the motor. On a brushless motor the torque will be MUCH higher and will depend on your Battery's ability to supply enough current. That's why brushless ESCs have a punch setting ie there is so much torque that you'd want to be able to adjust it depending on your gearing. If you're just spinning the tires then torque is the least of your problems.
With that said you're likely going to get an increase in motor temps regardless which route you take.