On Lupo80days they were able to reach average fuel consumtion of 2.38l/100km on average speed of 85,6 km/h with "stock" car when going around the world. I could hypermile my Lupo to 2.4 at those speeds behind a truck. They speak german on those pages so I cannot estimate have they drafted and how much if they have.
VW LUPO 3L TDI - In 80 Tagen um die Welt