Thanks, but you're not telling me why. The primary pressure modulator is the outflow valve. Above FL290 but below- and including FL370 it regulates to a differential pressure of 7.8 psi, and when climbing above FL370 it regulates to a differential pressure of 8.35. All is, as you mentioned, below 8.7 psi.
Other than that you seem to contradict yourself.
Let's say you set 370 on the FLT ALT-selector and climb to FL400. Why may you get an overpressure situation?