I know a lot of people are interested in this subject so here are the results of a recent trip. I went fron South Bend Indiana to Kansas Mo. this last week. Going I went on US 24 which is mostly 2 lane. I averaged 22.3 at an average of 50.6 mph. This included many towns that I passed through at the legal speed limit plus some diversions to see and photograph interesting thing. Plus 30 or so miles across KC in city traffic. I returned via I70 and I55 with the cruse set at 78. I saw my overall average go to 23.9. In Illinois I left I55 and took some back roads to avoid all the construction around Chicago. My overall was 22.9 at an average speeed of 57.7 mph over a total of 1336 miles. I have an 04 M6.