I weigh about 200 lbs and find a setting on the rear shock of about 150 psi works well on rough single track. About all the manual suggested was adjusting the rear shock so it sags by 1/3 with you on the bike. I keep my tires around 45 psi to absorb hits and maximize traction. If I go with lower tire pressure it usually causes pinch flats.
Pressure on the rear shock has not seemed to be a critical factor unless I have it extremely low (@120 psi). Max rated pressure is @300 psi
Do check your spokes frequently.
Mike
NeoJumper 2014, 26"