Any car at high speeds will consume fuel energy faster. Driving fast decreases range much more than driving slow due to the fact that air resistance increases as a square of the velocity.
The best speed to optimise your electric car's range on the motorway is approximately 60mph, but it's perfectly fine to drive 70mph too.
It's good practice to plan the charger stops on your journey before setting off. At the very least, it gives you peace of mind. As a tip, use Zap-Map to plan your route. It works out your recommended charging stops, based on the route, model and battery size of your EV.
See also: https://electrictogether.com/get-help/how-can-i-get-more-range-out-of-my-ev-
Tesla also has a good guide on range and driving tips here: https://www.tesla.com/en_GB/support/range