Good thought on the rating. The only thing I've seen rated for 40 or
50 psi is food grade polyethylene tubing.

Rudy wrote:

Are you sure its rated 40# ? Where did you get this idea ? Is there any of
your piping accessible, say in bsmt or crawl to recheck? Perhaps its a 40
oC rating for temperature rather than pressure.
Ours is rated 100# @ 180 oF and 160 # @ 73 oF
We ran 85# in our last house for 5 yrs and 70 in this one.

My home circa 1999 is PEX and the only thing I dis like is the 40 psi max
pressure for it.
I like stiff showers. I would have preferred that copper was used for the
rear outside hose bib, showers, washer. The bathroom sinks and toilets get
enough water with the 40 psi. I guess you could always run 3/4 instead of
the 1/2 or 3/8 that I have to get more volume.