my results
North of NYC to watkins glen 200 miles
lightly loaded,1800lb car on open trl 70mph-12.9mph

NY to FL 1265 miles
moving-loaded floor to ceiling,front to back,1800lb car on open trl
67mph-11.4
69mph-11.1
74mph with both a/c 10.2
78mph with both a/c 9.7
the first two tanks included sitting in traffic for about a half hour each so they might be a bit higher
jerry