Stay inside the
vehicle manufacturer specifications for tire pressures. Ever since the Ford Explorer / Firestone fiasco of a decade ago the testing of tires, the determination of pressures-versus-loads, etc, by the automakers has made them serious about the relation of tires and suspension in handling dynamics.
Better ride quality? Yes, but to stray outside the parameters (in reading tire engineer
CapriRacer's website
Barry's Tire Tech) is to invite "unexpected problems" in certain situations (my reading and word choice).
Longest tire life -- [1]] given the expense of premium tires; and, [2] the
absolute centrality to safe road performance of
predictable vehicle dynamics based on the interplay of tires & suspension -- is worth more on several fronts than the small mpg gains of "over" inflation.
That said, a few pounds to the good isn't seen as detrimental.
Where that point lays needs some experimentation (load versus pressure as in per wheel scale weights for a given loading of the vehicle).
If one knows the best pressure for solo commuting . . and knows what it is for full passenger and cargo load at highway speeds in high heat, one probably knows the percentage change (not number absolute) as well. This is worth finding, IMO.