Fixer, color me skeptical (not with your or your personal account, but with the PX4 in general)...After the 8357 Cougar, I'm pretty soured on Beretta's approach regarding the rotating barrel concept, and view the PX4 as pretty much the same mechanically as the Cougar. ToddG has had some experience with Canadian border guards whom have been issued the PX4, and at least anecdotally the reports aren't good, apparently with the guns continuing to have a tendency to seize up under use; hopefully he'll chime in here, or PM him.
The PX4 may be at its best in 9mm, as opposed to the higher intensity, quicker pressure spiking .40. The boys and girls over at the www.berettforum.net seem to love 'em, other than a previous "trigger stinging" issue, but that's more of a hobbyist/low intensity use forum.
Regardless, and especially with a PX4, I'd take DocGKR's advice before dedicating a PX4 to defensive carry use: Run a thousand round through one first as a reliability check-if there are hiccups, the roundcount restarts at zero; if it passes that, run at least(and I'd suggest 200 rounds is a more realistic minimum, but hey, ammunition being what it is today...) a box of your carry ammunition through it. I'd also heavily lube the cam tooth and barrrel areas where there is metal-on-metal reciprocation/torquing with TW25B, and apply adequate lubrication to the other areas appropriately.
I currently have, and run fairly heavily, a Beretta 92D (including at our recent IDPA State Championship Match last weekend-the gun performed superbly). I have not been tempted to venture into the realm of the PX4. YMMV...(and it sounds like yours fortituitously has to date).
Best, Jon