Pistol Grip Only shotguns are such a huge -- HUGE -- negative compromise in shoot-ability and hit accuracy/speed that I'd never consider one, for anything, unless the very most important factor was that I had to store it in the smallest possible location.
We've had a whole lot of threads on what value, if any, a shotgun with a "PGO" might have (including our late, wonderful, Moderator Dave McCracken's "PGO Challenge" thread which no one ever took him up on) that many will cringe to explore the idea again.
Basically, if you're going to carry such a thing for defense, accept that your LIFE is on the line, and take the question very seriously. Go get a shot timer, and some targets, and actually test yourself out, full-stock vs. PGO. Remember that the real challenge you're facing (assuming bear defense) is to repeatedly hit a softball bobbing and weaving wildly as it charges you at 20 mph.
Putting a slug where it needs to go (or a shot charge, if you believe that would penetrate enough to help) with a full-stocked gun is not easy. Attempting to do so with a PGO is probably not something you'll be happy with.
3 lbs. is a lot, and I'm really surprised that you drop that much weight, but I wouldn't make that trade, having spent quite a bit of time behind both types of stock.