Not sure what you mean by 5-7 psi vacuum? I guess you are referring to this...I usually only pull about 5-7 PSI, as I think that being gentle helps both the mead and the vessel. And I make sure to only do it on a relatively full vessel, as I am concerned about collapse. I know that there are folks who pull a hard vacuum on glass carboys successfully, so far I haven't had any issues. That's also what prompted me to get the gauge. I wanted to *KNOW* how hard I was pulling on it.
Also the tiny vacuum pump takes several minutes to pull down the pressure, so it's not an instant change.