Okay, time to interject here.
There's a minimum amount of energy needed to climb a hill.
Then there's the minimum amount of energy to push away air molecules at a given speed.
Energy to climb hill = The sum of both of those.
So, yes, speed matters, but there's going to be a minimum amount of energy necessary to lift weight up a hill, regardless if you're going 0.1 mph. Tall hill+lots weight = the minimum is going to be A LOT of energy.