It will be interesting to see just how efficient the EV is at what will be a lower average speed. I'm beginning to believe that keeping between 65 and 70 on Motorways is best for range, but it is a tad tedious. OK in bad weather here concentration is needed, but in good conditions the temptation to have fun, either speed or silly acceleration, is so tempting....
On any trip where you are expecting to require a Supercharger stop there is no advantage to extending range by going slower than you would normally drive. The reason is that you can always Supercharge at a faster rate than you can drive. The extra percentage used is put back into the battery very quickly. The only scenario where it's advantageous to squeeze range to the max is if it enables you to avoid a stop altogether.