From the factory, a 5305 motor is wound with 4 pieces of 21awg wire wrapping around each tooth 5 times. 21awg wire has a x-section of 0.412mm^2, so the combined 4 strands have a x-section of 1.648mm^2, or roughly equal to a single pass of 15awg wire.
The 5304 motor uses 6 pieces of 21awg wire wrapping around each tooth 4 times. Combined x-section of 2.472mm^2, or roughly equal to a single pass of 13.5awg wire.
The 5303 motor uses 8 pieces of 21awg wire wrapping around each tooth 3 times. Combinded x-section of 3.296mm^2, or roughly equal to a single pass of 12awg wire.
Arlo- I believe you could take square/rectangle wire with a x-section of 12awg (depending on how sloppy the factory windings are, maybe possible with round wire as well), and get the same 5-turns with it that you're using now. This would mean identical torque per amp for your motor, but HALF the winding resistance! This would be a huge improvement in power handling and top speed. It should mean roughly ~50% higher power handling for the motor, and a ~100% increase in continuous torque capability over a factory 5305.