I think something to keep in mind is that robots are still very, very widely used for processes lik spot welding and pick-and-place applications, i.e. processes where you generally want the movements to happen as fast as possible. Controlling the speed beyond that is not really a factor.
In any case, 100% is the full speed of the slowest axis involved in a movement.
With a recent software version that supports SPTP and SLIN movements you sometimes can also get better speed ramps. And for CNC using KUKA.CNC, but that is a complex piece of software.
In general, for smooth movement run the robot in T2/AUT at 100% OV (i.e. full programmed speed, not necessarily maximum speed).