  This article reports on a growing body of observational evidence that many
powerful lobe dominated (FR II) radio sources likely have jets with high
efficiency. This study extends the maximum efficiency line (jet power $\approx$
25 times the thermal luminosity) defined in Fernandes et (2010) so as to span
four decades of jet power. The fact that this line extends over the full span
of FR II radio power is a strong indication that this is a fundamental property
of jet production that is independent of accretion power. This is a valuable
constraint for theorists. For example, the currently popular "no net flux"
numerical models of black hole accretion produce jets that are 2 to 3 orders of
magnitude too weak to be consistent with sources near maximum efficiency.
