I have wondered about this too, but unfortunately I came to the conclusion that there is no simple answer because there are way too many other variables involved- how the vehicle is used, the design of the engine and its inherent weaknesses, which specific engine part we are discussing, etc.
A lightly loaded vehicle with an adequately powered engine constantly driven at high ish speeds on perfectly flat roads may see the best overall engine longevity with the taller gearing since the load on the engine should be pretty low anyways.
A vehicle loaded more heavily and/or driven at the same speeds on hilly roads will likely experience less overall engine wear with the shorter gearing since it won't be loaded as heavily while climbing and will have more oil and coolant flow relative to the work it's doing.
An engine known for wearing out its valvetrain first MIGHT last longer with the taller gearing since the valvetrain isn't directly affected by the engine's load, but rather RPM. There's no guarantee this would be the case though, other less obvious things like oil splash, the inertial forces on the valves, etc can have less obvious effects.
On the other hand, an engine known for wearing the bottom end bearings prematurely would likely benefit from the shorter gearing to keep the load down since higher load seems to wear the bearings more than higher RPM assuming the engine isn't over revved.
The engine is going to be generating the same amount of horsepower and doing the same amount of work either way. Whether generating more torque or spinning at a higher RPM would cause more wear will certainly be specific to that engine design and its usage conditions.