[IndyIan]

Originally Posted by dcb

Do you have a source for this? Anytime the converter isn't locked up there are hydrodynamic losses.

This lists the automatic as %5 to %15 less efficient (not %1 to %2):
http://en.wikipedia.org/wiki/Manual_transmission#Benefits

Some automatics do lock the converter in every gear now, some don't of course. Its hard to generalize these days about transmissions, so many variations now.

Back to the original question, it would be good to have an oil pressure gauge so you could see how oil pressure varies with rpm, or even using very light oil like 0W20. Since most cars don't have one I imagine most cars are pretty safe using 1/2 throttle or less at any rpm over idle speed.
Ian