MY holding tank presure switch is 4 ft. Below ground leveland rises to my module home would a 40/60 be better the my 30/50. To maintain good pressure

Ted, the pressure switch does not maintain the pressure, the pressure tank does. You will match the switch to your tank settings. So for example, if your tank, while completely empty of water, is at 38 PSI, then you will need a 40/60 pressure switch. If the tank is at 28 PSI of air while empty, then you will need a 30/50. What you want the tank's pressure to be set at is your personal preference.