I think that our cars lose about 16%-18% on the average, compared against the newer cArs that lose about 12%-14%, compared to the older early to late '60's high performance cars that lost about 25% such as the Mopars, probably due to variations in transmission & drivetrain improvements, but primarily tranny improvements, I think. The high loss for early '60's high performance cars is for automatics. I don't remember ever seeing how sticks compared.
Just from what I have read & talked to peeps about, too.