However the NEMA 17 with a proper gear reduction has plenty of torque.
Are you sure?
The motor and gearbox you linked can produce only 30 kgcm of torque continuously, which is 2.94 Nm. It is almost always best to oversize parts like this.
With 51:1 gear reduction, it is unlikely that you will find microstepping useful. Microstepping is mostly used to avoid resonances at certain step rates.