Under Wing Engine Efficiency

[Niallo]

Most two engine airliners have the engines slung below the wings, so does this mean that the thrust line is below the aerodynamic centre?
In steady flight, does a thrust offset from aerodynamic centre mean that aerodynamic forces must be used to compensate? If so, is the resulting loss of efficiency due to the added drag significant? Or to put it another way, are tail mounted engines more efficient?

[Intruder]

The tendency of the engines to push the nose up is opposite the wings' tendency to push the nose down due to the center of lift being behind the CG. Therefore it would reduce the downforce required on the tailplane and increase efficiency a bit.