Most buses in, say, Gateshead, are going to end up with a hilly run, regardless, though.

And you can equally argue that those routes with long, fast inter-urban stretches, like the prince bishops, pronto and even angel already have a mix of different paces and challenges on their journey - they spend as much time in nose to tail town or city traffic as they do stretching their legs. I should imagine that if you compared buses of similar mileage, rather than age, those doing long distance routes would probably be in better condition than those doing mostly stop start routes at fairly low speeds.