Greetings . . .
Here's a link that I found really useful in getting one's head around pumping loss:
StraightDope I am big fan of practical stories.
And here's some links showing empirical data that lower RPM is the place to be:
TDIclub MetroMPGThis is where I am coming from when I vote for lowest possible RPM and a decent throttle position equals best economy. As the desired cruising speed rises the need for OD becomes evident.
regards,
stock49