The Perennias & Prevails are slightly different, with a redesigned forged action. The trigger group/hammers are removable in a unit from the action once the buttstock is off, whereas on all the other 68x guns, it's all integral. The butt stock does not have a conventional through-bolt, but rather is attached by a device (Beretta calls it the "Q-stock") that intersects with a receiver stud extension accesible from inside the pistol grip.
From a quick inspection, the frame dimensions and locking/extraction systems seem roughly the same height & mass as the 68x guns, although the exterior frame contour cuts are quite different in shape.
So yes, the "P" frames are different.
The 68x series of guns are all mechanically - basically the same, notwithstanding some may have false sideplates, replaceable recoil shoulders, different finishes etc.
Price-wise the Perennia & Prevail will be very close, positioned more than the 686 and 687 Silver Pigeons, but less than the
682 Gold E's.
The 687 EL & EELL Gold Pigeons are more expensive still.