I’m planning 2 longer journeys >500 km with my not very economical 2001 Volvo S60 2.4T. I want to get to the finish as cheap as possible and also buy a slightly longer travel time. So I’m probably driving at night with cruise control at about 120 km/h, because the on-board computer shows the lowest relative consumption here. Does it make any difference what fuel I’m fuelling? Thank you very much!