The way I think about gearing and the effect it has on the motor, spead and torque is to liken it to gearing a bicycle. The bigger the crank sproket the harder the rider has to work to get the bike going, but once he gets going he can get a really high top speed. In other words, little torque at the wheel but better top speed. The opposite happens when the front sproket gets smaller.
Another way to think about it in very simple terms is the closer your gear ration gets to zero, the higher the top end and the lower the torque. As the gear ratio gets larger the top end decreases and torque increases.
With respect to the motor temp, the harder the motor has to work (lower gear ratio) the more current it draws and the higher the operating temp.
Of course, if I'm blowing steam in the wrong places, please correct me.