What pressure rad cap?

65Valiant310. All my research on radiator caps tells me higher pressure does
not help run cooler. It just raises the boiling point approx 3 deg. per pound.
i.e. 10 lb cap = 30 deg. rise = 212+30 = approx 242 deg. to boil. My 51 Nash
street rod never has run hot and I have a 4 lb. cap. My 65 Valiant with a
built 360 runs a 13 lb. cap as per the spec. for the truck rad. in it.