9-11. Loaded doesn't make a difference, but wind does. 15 mph Tail wind is 12+ mpg at 70 mph. 15mph head wind is 9mpg at 65 mph. Heading across northern Texas into 40 mph wind is about 6 mpg at 62mph WOT for 4+ hours.
Special Thanks and Recommendations to;
PAC Racing Springs
Joint Clutch and Gear