Adam,

If you really want to nail down the optimum number of hours for oil changes use oil analysis to determine when the oil needs to be changed.

These people have a very good reputation, but there are many others

http://www.blackstone-labs.com/

They send you a kit and information on how to collect the oil and their reports help you spot trends. I do 100 hour oil changes because on my cars with trip computers I find that my average speeds always seem to be around 40 MPH unless I take an exceptionally long trip on highways. I change oil in the cars around 4000 miles so it works out to about 100 hours.

In the plane I change oil at 35 to 40 hours but that engine is working harder.