Do any of you know what the required water pressure is for most RO units ?
I had one years ago and it seems that it required at least 50-60psi to operate.

40 psi is bare minimum with 60-80 preferred. The lower the pressure the less efficient it is and at about 38 psi it will not make water at all as it cannot osmose of pass through the membrane. Booster pumps are not that expenisve and pay for themselves quickly in water and DI resin savings.

I wouldn't run it more then 75psi. You will mess the membrain up. So I run mine @ 60-65 psi.

Pressure does not harm the membrane, quite the opposite in fact, they are safe up to 150 psi and higher. They also perform better at higher pressures. The only limiting factor is the housings and fittings, many imported units use Chinese knock offs and the pieces are not ANSI/NSF or UPC rated so may fail at higher pressures. Most name brand units do not have that problem since they use NSF and UPC components. Kache you may want to do a little research first before making statements like that.