Midway USA's loadMAP says Maximum Average Pressure (loadMAP -get it?) for standard 9mm P is 35,000 PSI. I've read "Plus-P" is supposed to be 38,500 psi. The "Plus-P-Plus" ammo I've seen has a label claiming it's loaded to 40,000 CUP, which while it's not the same as 40,000 PSI, is mighty hot. NATO spec 9mm is also said to be hot, but I believe pressures are measured using CIP (European) standards, which produce different numbers than SAAMI.
The 38,500 psi figure above came from an Internet chat room, so judge for yourself its reliability.