I once asked a stemm-importer about the pressures for stemms.
The information I got was that the stemms are tested to stand the pressure-rising from 18 dgr C /65dgr F to 100dgrC wich is boilingpoint of water, convert it yourselves. This can happen incidentically by the heat of the brakes transported trough the rimms. The maximum pressure of normal rubber snap in stemms ( the 400 series) is 4,5 to 4,8 bar ( 65 to 70 psi ) at 18 dgr C/65F filled, and an extra pressure by temperature rising of 1,8bar/26psi they are tested for at the mildest american standard.
Thought it might be interesting to know.
The 1 psi at 10dgrF rising is a rule of tumb, wich does not go for larger temperature or pressure risings. I once made a spreadsheet for playing with the temperature and pressure, and filled in the 50 to 60psi rising rockport gave
here the picture
Mind that what the tpms gives is not always accurate