Incorrect. If properly set:

A 30/60 set tank would have an air precharge of 27-28 PSI.

A 40/60 set tank would have an air precharge of 37-38 PSI.

So, the 30/60 set tank, starting from 0, will start accepting water into the tank at 27-28 PSI, while the 40/60 set tank won't accept water until 37-38 PSI. Thus, the diaphragm or bladder *will stretch more* on the wider setting. Whether that's bad for the diaphragm/bladder depends on the details of tank manufacture. Most are happy to be set at 20/40, and that should be the "same stretch" as 30/60, 40/80 or 50/100. 20/100 would be "more stretch" and might well break something. The max pressure has to do with the outer containment vessel, not whether you've broken the internal bladder/diaphragm/membrane.

All of which is irrelevant to solving your perceived problem with modern technology.
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You want ***city-like constant pressure.*** 

You can purchase **variable-speed pump controllers** (variable frequency drives) that will give you city-like constant pressure, or a lower-tech and (generally, at present) somewhat less expensive **pressure-regulation-valve thing** (which I refuse to shill the most widespread version of by name, but I believe they have bought a shill-space on the forum you looked at, so you'll have no trouble finding them) that will get you near-constant pressure after one drop to the lower setpoint to turn the pump on, so long as you are using water at a sufficient rate, followed by one excursion to the higher setpoint (slowly) after you turn the water off.

Both of those will work with no increase in your present pressure tank size, and they will work with a much smaller pressure tank if/when you need to replace your pressure tank or are building a new system.

You could also go older tech and run a bunch of pressure tanks from 60-80 (or perhaps 60/120, but that might be impractical from the pump and pressure on the down-well pipe point of view) into a pressure regulator set at 50-60 output, but that would be much more costly in terms of money and space required.

See also: https://diy.stackexchange.com/a/62696/18078