Calculating the winding equation in a bldc motor
TL;DR  The torque is independent of the gauge of wire and number of turns, other things (winding volume, heat generated) being equal

This applies to BLDC motors, electromagnets, transformers etc.

Imagine the winding space is wound with two identical windings. Pass the same current through each. 


Each winding will generate a certain amount of heat.
Each winding will generate a certain amount of magnetic field
Each winding will generate a certain amount of voltage if the field changes


Now we have a choice whether to connect these two windings in series, or in parallel.

If we connect them in series, then a total of one winding current flows, and the total voltage across the windings is twice that of each individual winding. The total number of turns is twice that of each winding.

If we connect them in parallel, then a total of twice the winding current flows, and the voltage is the same as the individual windings. But note, this parallel connection is effectively the same as a single winding made with wire of twice the area. The effective number of turns is the same as the number of turns on each winding.

This means that we can change the number of turns and the wire gauge, keeping the volume of copper constant, and get the same heat dissipation, the same magnetic field, and the same electrical/mechanical power (volts goes up, current down in the same proportion) as before.

Changing the number of turns and wire gauge has changed the impedance of the wound device. Double the number of turns, half the current, impedance which is volts/amps has increased by a factor of 4. Generally, terminal impedance goes as \$N^2\$ where \$N\$ is the number of turns on the winding.

The maximum torque and speed of a motor has to be designed in magnetically and mechanically, as changing the number of turns and wire gauge only changes the impedance.