From what I've been able to gather, the maximum values are a "best case" scenario, and cannot be expected from multiple joints at the same time. The motion descriptor only has a singular "vel" parameter which is applied to the joint that is moving the furthest and all of the other joints will move at a percentage of that. So using the nominal velocities would be my recommendation.
@marshallpowell97 wrote (in https://github.com/ros-industrial/staubli_val3_driver/issues/2#issuecomment-584335689):