Just kibbitzing here, but I don't think I'd attempt a 50 yard shot under pressure with any handgun unless there was absolutely no alternative, let alone 100. Better to take cover, reload, find a long gun, etc...
Unless someone had bet a beer on it, that is. It ain't what you're throwing at them that counts, it's what you hit them with. Mark makes a great point. If I might expand upon it a bit, if the other guy has a deer rifle, he's going to kill you if you stand up and try to take him out with a Hail Mary shot out of a handgun. It's probably best if you think through the multitude of possible scenarios you might encounter where you need to bust a cap in someone's *** and work from there. In my house it's CQB, in the yard it's nothing over 30 yards where I'd HAVE to shoot, and around town I figure the guy is going to already be on top of me. For that reason, I fully support your decision on a subcompact back-up. Something you can stick in their gizzard and unload.
I like the idea of having 37 rounds at the ready, so I carry an XD9 with a spare mag loaded with 147 gr +P JHP, and a .380 loaded with ball ammo (Penetration issues there, so no HP in the mouse.) Bigger is better, until you run out of ammo.