I found it really depends on climate control and type of driving. Before TX heat hit and driving almost never on freeways, I was near 4.5 after very closely adhering to basics for improvement. Now I am near 3.8 with AC on all the time. If you make long commutes at 55, it will be 10 per cent or more higher. One afternoon trip up the Tollway to northern suburbs for a dental trip and return at near 60 lifted my month 10 per cent. Consequently you can only compare yourself against cars that go the same places you do. Somebody that commutes 60 miles a day with little city driving on the Tollway could blow through 5.
2013 SL Blue Ocean
Bought used, March 2015 12,764 miles
4th bar drop 56 month, 20,200 miles, AHr at 42.1
Appears fully loaded
Condo home, Using public charge except in emergency
Dallas, TX downtown, shaded non-temp controlled garage