PEX can handle a lot more than 70 psi - over 100 psi for sure.
Residential faucets and fixtures have an upper limit of 85 psi- don't know about RV faucets.
Winnebago tests their motor home plumbing systems at 85 psi.
Because of a malfunctioning Watts whole house regulator at the house we bought summer before last, our motor home saw 135 psi for three weeks with no problems.
I don't know how long the house saw the 135 psi - at least a year though.
I didn't test the pressure at the house because I saw the Watts regulator - also didn't connect the one I have for the motor home - same reason.
The new Watts house regulator is set at 65 psi as is the Watts regulator I use on the motor home when the pressure is over 65 psi.
Clay (WA5NMR), Lee (Wife), Katie & Kelli (cats) Salli (dog).
Fixed domicile after 1 year of snowbirding and eleven years Full Timing in a 2004 Winnebago Sightseer 35N, Workhorse chassis, Honda Accord toad