Have 8000k on my SI at 5k put full synthetic Mobil 1, since then been getting almost 400 miles/ 650km per tank usually 9.3gallons/42L to fill so getting in the 40's most of time and not driving as a tender foot. I take the car into vtec at least once a day. But i guess its all in how you break your car in.
Use to have a 2002 Civic LX before this, I got insane mileage with that car also 52 mpg constantly.