Do you all remember why the 40 came to be? CIA in Miami shot some cuban drug peddler all jacked up on coke with the standard issue 9mm, after 18 hits he was still running and returning fire, so the 10mm was developed, but to much recoil for the pansy cia guys so the powers that be shortened, the 10 to the 40. Me I carry either a 45, or a 10, have an AR with a 30 round in the truck, another with a 100 rd. drum by my bed.
there were several reasons for 10 and 40
bullet technology has changed some of that
early use of 147gr 9mm and even current use of 147gr 9mm. I have shot raccoons with them from a glock 19 these were the Winchester Ranger T , might as well have been fmj for what they were doing/not-doing to coon. that is a 15-20 pound animal that doesn't know it is dead till it is but dispatches well with a 22lr-hp
the barrel on a G19 is 4 inches that is about the most common length of pistol barrel there is if you don't get good expansion from 4 inches of barrel and a target a few feet away it seems like a poor ammunition choice and I never got any more.
I carry 124gr xtp in my 9mm pistols the racoons told me it worked the best. no it isn't the fanciest bullet I am sure there are better but they are reasonably available and at a price I could afford more to test and practice with and carry and use up and rotate in fresh
you make the point I was going to bring up this morning after thinking about this more
the OP asked about 9,40,45 in a full size gun so my answer was he had 9 he already stocked 9 the differences in performance are not that great and the capacity and ease of shooting is a benefit
however , a short over all length long gun might be the better option for in house.
reasons for a handgun for In home SD situations
Pros , you have a hand free you can get doors , you can grab kids and drag them to your safe spot , and they are short going around corners
Cons, most people don't shoot them as well , as fast or as accurate as a long gun ( we see this in the same stage non GM PCC shooters are running GM grand master pistol shooter times and hits on the same stage.)
other things to consider you will have what you have when you pick up your rig whatever it is if it is a pistol maybe you will have it in some sort of a bag with extra mags and such but likely not which is why a mounted light is a good idea for any bump in the night gun , positive identification is huge
you may very well end up fighting in exactly what you were sleeping in seconds earlier birthday suit or not.
pros and cons of long guns
Pro, more power , often more ammo capacity , better accuracy and control
Cons , longer , harder to move with
shotguns lack ammo capacity but hopefully what is in the tube is enough those of use who have had one in our hands since we were a kids shoot them very well.
anything powerful to get the job done well goes though house hold walls be it handgun , rifle or shotgun. some ammo types are better at not going though the second wall. so that has to be a plan where people and the best answer seems to be make sure the projectile passes through the bad guy first they slow down projectiles better than walls.
a miss with a super-magnum is still a miss better to get hits with the thing you can get hits with well and fast. the better the hits the better anything works.
long guns need a sling typically we say hand guns need a holster to be complete
I like a long sling you put over your body but can still move with like a Blue force gear Vickers or the magpul ms# or something similar that has the rapid adjust so you can go loose to snug so you can be hands free. as well as switch shoulders should you need to.
long guns also need a light I run a very basic Surefire it turns on and off no other features
there isn't really a magic round only good placement and follow up till it works
I hope you never need any of it.