I'm with you Soren. I've had this debate with others, often over "Brand A fuel gives me better MPGs brand B." There are too many variables to pin it down to a few hundred miles on this then that in real world conditions. I usually get in the low 40s on my Speedmaster, but on a recent long haul, I was clocking MPGs in the low 30s, for a number of reasons, mostly related to slab speeds and a tremendous amount of wind during most of the trip.
I contend there's no way to know accurate MPGs without a very lengthy comparison for starters.
The EPA method of determining MPGs for autos (measuring exhaust discharge while on a dyno, performing a programmed run) is very close to worthless IMO when compared to real world vehicle operation.
http://www.nytimes.com/2006/01/11/automo...nyt&emc=rss
The method to determine comparative MPGs that seems to be the most reliable is to operate vehicles in controlled conditions, then weigh the remaining fuel at the end of the runs.
