I tend to stick to the speed limits on the roads unless like you say it's a very quiet road. There is a lot to be gained by going the back roads in a electric car 80kmh speed limits vs 100- 110km on the freeway.
That said my most economic run on my regular 104km trip i do was going the freeway steady 100kmh (perhaps there was a tail wind) and my most consuming run I have done was going the back roads . I got every single red light and train crossing you could get , stop-start,stop,start each time you have to get that weight moving again chews energy.
Offgrid 2008, Selectronic PS1 6kw/48v inverter, x 2 Midnite solar classic 150 MPPT, 3960w NE PV 24 x 165w BP panels, 4200w NW PV 21 x 200w DAQO PV, 16x400ah lithium.