More phase inductance in stepper motor
A higher winding inductance means you will need a higher voltage chopping driver to maintain torque at higher step rates where inductance extends the current rise time each time the motor steps.

It's not uncommon to use for example a coil with an ohmic voltage rating of less than 4 volts with a chopping driver backed by a supply of 12 volts or more.  Conversely, a 12 volt rated coil will have very little torque at speed when used with a driver which can only apply 12 volts.

The same motor chassis is usually available wound in different ways.  For performance you generally want to chose the lowest inductance configuration, which is typically also the lowest coil resistance or ohmic coil voltage.

That said, if you're buying something through a discount/surplus channel, you may not be able to select the ideal configuration.

You should also consider if you are getting full rated current through your existing motor before replacing it - it may be that what you really need to replace is the driver.  The most informative way to really evaluate this is with a scope on the driver's current sense resistor while commanding high step rates, but the driver's manual may give you instructions for setting the drive current by theoretical means.