My truck gets driven in the dirt a lot so my tires are normally pretty low unless I have to drive to drive a long distance. Right now they are at 25 in the front and 20 in the rear. For highway driving I would put them at 35.
I went to 38 yesterday on a trip back for Oklahoma. Ran great on Hwy but on city roads, the extra 3 lbs from 35 was way different. Much smoother on city roads and bumps with 35. A much better ride IMO.