All new RVs come with PEX plumbing.
PEX tubing is rated up to 150 PSI.
However the factory facets & bypass valves are not rated for that much.
Your only as strong as the weakest link!
The standard recommendation of 40-45 PSI comes from the older gray tubing you find in older RVs & mobile homes.
The gray stuff had a max rating of 45 PSI.
I replaced all my factory facets with residential ones from Lowes.
I keep my regulator set to 55-60 psi & have had no issues.
Dave, Judy & Daisy May
2010 Sierra 356RL
2011 Silverado 2500 4WD, LT, Ext Cab, LB
Duramax 6.6L V8 Turbo Diesel
Allison 1000 6-Speed Automatic Transmission