For a given load, the current needs to be at a certain level in order to not miss steps. These things are consequently to one another, so its not so much liberty in setting current to a low level. That would be the place to aim at when adjusting the current anyway, so it goes without saying.
If you want to avoid the audible noise, get a driver which has "more knobs" than just vref. For example drivers which let you also set decay in whatever mode you want. Also some other drivers let you adjust some parameters related to frequency. For example if you try to use a driver like "stepper motor driver 3.3" that will let you adjust much more than a pololu. Better chances to have it run least audible when you can adjust almost everything. I dont think they make that driver version anymore, but i think would be a good one for the purpose.
The nema size is just the faceplate of the motor, i dont think the external geometry of the motor would matter, e.g. be it nema17+extra long or nema23 normal. But i would personally go for nema23 if you want to run a higher load, just coz you can replace it later whereas the nema17+long probably wont have a direct replacement, for being already at the extreme of its category (that status usually has some implications of some sort).
If you want to avoid the audible noise, get a driver which has "more knobs" than just vref. For example drivers which let you also set decay in whatever mode you want. Also some other drivers let you adjust some parameters related to frequency. For example if you try to use a driver like "stepper motor driver 3.3" that will let you adjust much more than a pololu. Better chances to have it run least audible when you can adjust almost everything. I dont think they make that driver version anymore, but i think would be a good one for the purpose.
The nema size is just the faceplate of the motor, i dont think the external geometry of the motor would matter, e.g. be it nema17+extra long or nema23 normal. But i would personally go for nema23 if you want to run a higher load, just coz you can replace it later whereas the nema17+long probably wont have a direct replacement, for being already at the extreme of its category (that status usually has some implications of some sort).