Formulas:

Only the intercepts change for tires between 20-28 widths. Larger widths and the slopes change. Obviously these are generalized and assumed to be linear. While not 100% correct they will give you a great place to start.

Tire Width=20: Pressure(psi) = 0.33 * Rider Weight in lbs + 63.33
Tire Width=23: Pressure(psi) = 0.33 * Rider Weight in lbs + 53.33
Tire Width=25: Pressure(psi) = 0.33 * Rider Weight in lbs + 43.33
Tire Width=28: Pressure(psi) = 0.33 * Rider Weight in lbs + 33.33

Tire Width=32: Pressure(psi) = 0.17 * Rider Weight in lbs + 41.67
Tire Width=37: Pressure(psi) = 0.17 * Rider Weight in lbs + 26.67


Example: You are 150lbs running 28's

Pressure (psi) = (0.33*150) +33.33 = 82.83psi (rear)
Front Pressure = .9*Front Pressure = .9*82.83psi = 74.55psi front

You could start by running 85 rear 75 front and adjust from there. For your weight I would step down to 23's which you could run at 92F - 102R. That would be nice and comfortable and have less rolling resistance than the 28's.