Servo motor voltage

Hi,
I notice in the manual for the Gecko G320 it says not to go more than
5 volts over the rated voltage for servos. What I'm wondering is, why 5
volts? I'm building a supply for 60V motors and I found some 48V
transformers for fairly cheap. This would get me:

(48V * 1.4142) - 1.4V = 66.5V

Would this be too much for 60V motors? Should I add some diodes to drop
the voltage a bit?

Thanks!

C|