For every weight+tire there is a fairly narrow range of ideal pressure.
ideal pressure is in the eye of the beholder. mountain bikers run 15 psi and track racers run 150+.
appropriate pressure depends on tpi/rubber compound, rim width, intended use, and
personal preference. rim width, in particular, has a huge effect on contact patch. i personally run 25s on 19-20 mm internal rims and the sidewall is damn near vertical.