Water pressure question.

In general our water pressure is good, almost too good last year as it was well over 100+psi at downstream hose bib, but now after replacing a water pressure reducer that has failed after 18years it seems to be falling lower again. We adjusted after replacement but I think the city added some capacity in preparation for future housing around us so it is finally stabilizing. But my question is what is the recommended test method? I have a bib pressure tester but should it be tested with nothing running or with water running elsewhere in the house. When I have water running it drops to 40psi when it is not running it is around 65-70. I would like it to stay around 80 so I can run more than 2 or 3 things at a time and have good pressure but not damage some of the appliances in the house. Any advice appreciated.