For your theoretical "longevity" consideration:
(technology and engineering adequacy/efficiency aside)
...usually machines that operate in the least stress benefiting from the root engineering/ design will optimize longevity
From another perspective,
...usually machines that receive the least stress in terms of "use" will optimize longevity
From yet another perspective,
...usually machines that receive the least stress by benefiting from "over maintenance" and "timely" repairs will optimize longevity
Would be ideal situation to acquire an engine with all three characteristics (used), alternatively ideal to control the variables yourself (new).