I do not believe I've ever seen any documentation that shows an actual measure of +p+ being above SAAMI specs...
What I've been told, and have come to believe, is that SAAMI sets a true max for pressure. The manufacturers (big boys and their lawyers) load to a certain percentage. The +p is just a step closer to the SAAMI number, as is the +p+. I'm not sure I believe that any of the actually exceed the SAAMI number. Please, if you can show me i'm wrong, I'd love to see it, as I've been looking into this a while, and getting nowhere. Nobody in the "hot rod houses" openly discusses their pressure levels with the public. It's some sort of trade secret, I guess...
If the SAAMI spec on 9mm is 39,000, or whatever it is, I'd like to see some documentation that shows any of the +p+ loads above that. I'll bet even Double Tap and Buffalo Bore are at or below the SAAMI number.
I do agree that accelerating a bullet beyond it's intended speed actually can cause it to be less effective. Instead of the nice WIDE flower petal shape we want after impact, the added velocity can wrap the "flower petals" back over the base, making it less in diameter and less effective. Energy isn't everything in handgun ammo. This is well documented.
I'm not looking for a pissin' contest on this, just some proof, beyond a marketing ad, that proves that a manufacturer is willing to load a round and sell it to the public that is above the safe limits as set by the widely accepted reporting agency, SAAMI.