Depends on the seal manufacturer. Those numbers are usually provided through their engineering data system. Their data will be fit to a particular tolerance for seal race surface finish, which will be influenced by the reality of manufacturing.

Right, but are we talking closer to 5% or 50%?

Allow me to embrace my engineer nature and hedge my bets. A contact seal of that size is usually specced for a power transmitting shaft. An (assumed) 20" shaft is going to transmit a huge amount of power. So much that the seal losses will be negligible. Those same losses would exist on any shaft/seal combo of that size, but would take a greater fraction of total motor power, given the size and power constraints given by an internal motor design.