Nice detailed writeup. I formerly had an 03 HCH and now have the Accord. One difference I noted was that the Civic mpg gauge was always optimistic by about 10%. Others seem to report errors of about the same margin. (Actually, mentally taking 10% off the indicated mpg gave a pretty close-to-reality figure). The Accord gauge (in the dash) is very accurate. (The NAV guage reads about an mpg too high).

I hope they fixed this in the 06 Civic. If not, you're mpg might not be as good as displayed - hope that's not the case. It's very good in any case, especially for winter driving and a new engine.