Is the MOSFET (STP85NF55L) reliability affected if the Vgs is near to the maximum specified in the datasheet?

[IGent.1]

My customer specifies a relation of 60% of the maximum Vgs for operation. My design is using 80% of the maximum Vgs. They are asking how this increase will affect the component reliability (failure mechanism, failure rate...).

My design is eqquiped with 4 STP85NF55L, operating at 32Hz (PWM) resistive loads.