I’ve also done up to 60 mph on pave at 20-23 by the time it’s warmed up many many times. I try to stay under 55 in that case. Tires don’t even get hot. Obviously it’s not ideal and yes you “should” air up. It’s gets super loud on my Kanatis and yes it does roll hard. But for the brief 5-15 mile jaunt it’s not an issue during a day of wheeling.

28psi cold is very conservative to say the least. . Why even air down would be my thought. I think what’s important is go at the speed of your understanding here. If your really worried start at 25. Hell I’ve done 12.5psi in Moab before…. 18psi is a really nice all around pressure for a 10pr 265-75/16 3ply sidewall in my experience of trying all kinds of pressures.

For what it’s worth, I run 40 psi street and 18lbs that warms up to 20-22. Staun deflators are awesome. I also have an arb deflator. 5 people and gear always. 4.30 axles.