Hi awetmore. Arnold? Arthur? Andie, Audi? Allan? Anthony?
You don't HAVE to upgrade the 24V--The G540 will give way better performance even with that, but double the Voltage equals double the power. The idea is to get the Voltage as high as possible, but not to exceed 50V.
Stepper motors do not run on steady current, but pulses of current. Higher Voltage lets the coils charge faster during a pulse and hence more speed.
Your motors will run at LEAST twice as fast with 48V. If you get the Keling 7.3A PSU you can even adjust the Voltage up to the max 50V.