Depends on the manufacturer of the P+ ammo. I've chronographed 9MM from Cor-Bon & Triton, both are very fast. Faster than NATO stuff. Then I've tested Remington GS and Federal 9BP P+ 9MM and its barely faster than thier non P+ ammo. I mean we're talking 90 to 125 fps. more than their non P+ ammo. So in my experience its has to do with the manufacturer.
Cro-Bon & Triton are faster than NATO; other manufacturer P+ ammo is about the same or a little less than NATO 124gr.
Then again I shoot out of an HK P7M8 and the gas delay system may have something to do with it.