There are quite a few fairly small framed .45s out there. The first one to come to mind in that regard was the discontinued AMT Backup in .45, a darn nice belly banger, if you don't mind the 96 lb, long, stiff, creepy trigger pull.
Then there's the Glock 30 ( a slightly bulkier, but much better choice) (my 275 lb father carries a larger frame Glock 23 in his front pocket with no worry)
Then in the 1911 style there's the Kimber Ultra Carry, Para Ordnance P-10/ Warthog, and the Springfield Ultra Compact 1911. These are all in the $600-$800 range. There's quite a few more of this style, but I'm assuming you don't want to drop $1200-infinity on the gun.
In regards to understanding the potential of the .45, I would not rely on it to do anything more than any other handgun round. a shoulder hit is a shoulder hit for the most part, and the immediate circumstances and the attackers physique and mindset are gonna play a much more significant role than a few millimeters more or less on the diameter of your chosen projectile.
There have been cops killed by shoulder wounds recieved from a .25 ACP, and there have been attackers fatally shot in the heart or lungs that still managed to kill a chosen victim before croaking off.
That being said, I do like the .45 ACP marginally better than most self defense rounds, but to me caliber is one of the least things I consider (within realistic parameters of course) Reliability, ergonomics, and sights tend to be the most immediate priorities with caliber far behind. I myself carry a .45 ACP, but only because it's the handgun I own that I shoot best.
To speak very plainly, and perhaps controversially, I wouldn't sweat the search for the .45 There are alot of other guns out there that carry more nicely, function more simply (and reliably) and cost a heckuva lot less. a well placed shot is what will count, and there's only one kind of dead. (neutralized for the PC among us)
And let us not forget the first rule of a gunfight is to have a gun- get something that you know will not become an inconvenience in your day to day life. Make sure it's reliable, make sure you can hit with it, oh yeah, then consider the ammunition.
to give an offhand recommendation, I'd consider a S&W J-Frame revolver. If you want something light, theres the 14 oz or so .38 specials. if you want more horsepower there's the .357, weighing in at ten ounces more.
If you really want an auto, I'd still consider a 9mm or .40, for the sheer practical fact they fit on a smaller easier to live with frame.
I hope I've given ya' food for thought if nuthin' else. (I'll get over it if you think I'm full of feces too)
