Using your figures when converting to US gallons it appears you're getting just shy of 10 mpg. According to Ford that's at the extreme high end of what the V10 is capable of even in the lightest chassis.
When I asked a Ford rep how it was that some people were reporting 11 - 12 mpg his response was "Anyone claiming double digit gas mileage with the V10 needs to recheck their math". I guess he hadn't considered using the Imperial gallon as a unit of measure.
Considering the 1999 V10 was only 275 hp I doubt you'll be able to match the mileage with anything newer. The 275 hp version was only used in the 1999 chassis. The 310 hp version was introduced in 2000 and used until January of 2005. It was replaced by the 362 hp version which is still currently in use.
Our 2013 Adventurer has been averaging 7.8 mpg when driving between 55 and 62 mph while towing a 3750 lb. Jeep. If we were using Imperial Gallons as the unit of measure we would be getting about 9.4 mpg
A question as to where you are able to purchase fuel in the Imperial Gallon measurement. I thought Canada switched to the metric system in the early 1980's. We've traveled through Canada several times in the last few years and all our fuel purchases were measured in liters.