If you want to optimize for range you should apparently aim for holding a constant 50-55 km/h.
https://cleantechnica.com/2018/07/15/tesla-range-plotted-rel...
- preconditioning the battery & cabin while the car is parked and plugged in
- using one of the newer models with a heat pump
- turn the cabin heat down and the seat heating up
The first point is the most important. We often have little range loss on our way to the destination but significant on the trip home because we couldn't plug in at our destination and the car got cold.
That said, the Volt will warm the system with the ICE if it gets below -10C. But I've heard similar numbers from pure-BEV owners.
I think rather 80-90 km/h, at least for Nissan Leaf, as well as from the table you linked (55 mph ~~ 89 km/h)
However, for newer EVs the sweet spot will be at higher speeds, because those cars are able to recharge at much higher speed (at least 2 times faster).
The table doesn't show any data below 55 mph. This site: https://cleantechnica.com/2018/07/15/tesla-range-plotted-rel... has a graph that plots range vs speed all the way to 0 (for the Model S) and it shows the 'optimal' speed to be around 35 mph.