Is over-volting a motor just a little bit likely to affect its lifespan?
If you are going to regulate the current using PWM, the voltage of the pulses will not make much difference in the range of 15% or even 30% above the rated DC average voltage at this voltage level. The important thing is not to overload the motor. If you were to increase the average voltage by 15%, that would increase the motor speed by 15%. To drive a centrifugal pump 15% above normal speed requires 32% above normal torque and 52% above normal power.