Given these pump curves, what can you tell me?

for what you are after, no one can tell you anything from those graphs

Or is there another curve
(more/different data) that would be needed to answer my question?

very much so, you need one that has that curve and some kind of electrical consumption
curve(you could get the answer from almost any electrical curve), it would be nice to have
a MTBF curve added to that, another might be heat transfer.

when water moves slower thru a hot object it picks up more heat some of that is set, some
of it depends on what the water is moving thru.



There's definitely a "belly" to the curves and it seems that if you
chose a point where the area within the rectangle of the flow and
height is maximized, you may have found some sort of a sweet spot.

But is that sweet spot likely to have the lowest wear on the pump? Is
the pump likely to run most efficiently and produce the least waste
heat at that point on the curve? What might that sweet spot mean
to us as aquarists?

that sweet spot probibly doesnt mean anything, except where the most gph is. most
aquarium pumps dont list the data you want. some larger like 1/4+ hp pumps do.


--
Richard Reynolds