I am pretty sure in a discussion I had with Maurice at Gecko a few years ago he mentioned there was no problemĀ running dc brush type servos at 50% or so higher voltage than the motor rating, something to do with the way the amplifiers work , I know a couple of machines I have worked on in the past (mold handling equip) have had 90vdc motors working with 170+- vdc power supplies.
I know the old bridgeport I am working with came fitted with Reliant 90vdc motors and the original power supply is 177vdc.
I know very little about dc servos and power supplys beyond the basic wiring , just passing along past exp