I do the same type of racing at Silver State Classic. My 496 stroker would never go below 65 psi (above 2500 rpm) on the hottest days even with 220° water temps, but during Silver State, by 15 minutes in it would settle in at 38 psi at 4900 rpm. It really bothered me and I blame my eventual Crane Gold rocker arm failure on that pressure issue. Ultimately, I ditched the unbushed Crane Gold aluminum rockers for bushed chromoly Comp Ultra Magnum rockers and went to Brad Penn 20W-50. Last run I did not go below 60 psi.

That oil, when really cold (under 45°), will be slow to come up to pressure.