I find this very interesting, but one thing strikes me about this formula. As I did this for my two main vehicles, a 4 cyl 2006 Accord and a 6 cyl 2005 Pilot, I see that my Accord can go 73% more miles than the Pilot. (Accord's factor is 143.83 * C, Pilot's factor is 83.05 * C).
So unless the sump capacity is much higher on a lower MPG vehicle, the OCI will always be considerably shorter than a higher mileage vehicle. Not sure I buy this. According to this formula, auto manufacturers should have significant differences in there OCI recommendations between SUVs and cars for example.
Wouldn't RPMs also play a major role in the effort an engine puts out that would not show up in MPG? My Pilot cruises at 70 MPH at 1,900 +/- while the Accord does 2,300.
Just an observation.