I have a long trip from Keswick, Ontario to Niagara Falls, Ontario and back with 2 weeks of commuting; doing just 110km/h with cruise control, of which i hit 1148km and fuelled up with 55.2L.
If my fuelly does not pop up; my average for about 27000km is 5.7L/100km.
I avoid using cruise control now; and just try to ride the hills.
All of my 1000km tanks were gruelling, and now i just fuel up at about 1/2.
Always added Power Service, silver or white, but recently purchased some Archoil; hopefully it works out well.