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
MetroMPG

This 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