I run lower, 7 to 9 psi. Aired down until they show the slight beginning of a bulge at the bottom.
This is at the advice of my neighbor, a third generation orchardist around here, who saw my tires at the recommended minimum (14?) and commented that running them rigid hard gives up all the traction that an R1 is intended to provide. You want all contact area possible without ruining the sidewall. It seems to me also that with minimal air volume, allowing some flex helps prevent casing damage.
That is for the rears - the fronts need maximum specified pressure to stand up to loader use.
If you are running R4's, their sidewall may be to stiff to show a bulge at any pressure so I don't know if it makes a difference.