Voltage recommendation for slosyn kml063f07

I just picked up a bunch of Warner Electric (now Superior Electric?)
KML063F07 motors. I am in the process of designing my power supply
and was wondering if anyone had any recommendations for voltage. I
will be driving them with Geckos at 3 to 7 amps.

The specs on the motor are as follows:

Triple stack
Bipolar (4 wire)
350oz/in Holding torque
3.30 Amps
3.29 Volts
1 Ohms Resistance
5.20 mH Inductance

I have looked at the graphs on their website and they show
performance levels at 24 and 36 volts. If you have any experience
with these motors, specifically at what voltages they like to run
without overheating or loss of performance/life, any help would be
greatly appreciated. I will be using these on a moderate size
router/engraver.

Thanks,

Chris