1000 volt is usually more than enough...i test ALL motors at 1000 VDC. yes, even 115VAC motors and they do just fine.
Yeah, until you find one that the insulation is compromised. Industry standard for DC test voltages of 120-
240 VAC motors is 500 VDC. Certainly you can continue juicing those little motors to 1000 VDC until your luck runs out.
The manufacturers of 4160 V motors prefer a continuous application (10 minutes) of approximately 2500 VDC rather than shorter durations of 5000 VDC.