The amount of power required to maintain a speed goes with the cube of the speed.
It takes 65% more power to drive at 65MPH than it does at 55MPH.
It takes 250% more power to drive at 75MPH than it does at 55MPH.
It takes 800% more power to drive at 60MPH than it does at 30MPH.
ECO mode for EVs is "drive slower."
As far as your paddle stop question: the paddle stop exists so you can activate regenerative braking without pressing the brake pedal. When you press the brake pedal, the friction brakes engage in addition to regenerative braking, so you will always lose some energy to the friction brakes, which is less efficient. The bolt can only regenerate up to 70kW using the paddle, so there may be times where the brake pedal is required, but usually if you anticipate well, you can get away with using only the paddle brake, or one-pedal mode (which will regenerate up to 55kW).