My 500 S&W is one of the 4" models. It comes with two different muzzle compensators, one for jacketed bullets, and a separate one for lead bullets. The compensators do a pretty good job of keeping the muzzle flip from hitting you in the middle of the forehead. I might not have chosen the 4", except I came across a really good deal on one at a local gun show. I don't think the original owner was expecting just how powerful these are

. With the full-power loads, it's really in a completely different league than any other handgun (except maybe one in .50 BMG or similar), and it must be treated with respect. I know of a person who suffered a significant shoulder injury because he was unwise enough to lock his elbows when firing one. Most of the full-house loads actually exceed .45-70 rifle ballistics. I bought a pair of shooting gloves with gel-filled cushions just to be able to shoot this pistol without hurting myself. But it's a real blast to shoot! Just not a lot of rounds in a single session.
I'm also a huge fan of the 10mm auto, and have a number of pistols in this caliber, including a S&W 1006. The original Norma load of a 200 grainer at 1200fps is a huge step up from the .45 ACP. I've always wanted to add one of the S&W 610 revolvers in 10mm auto to my collection, but I just haven't been able to bring myself to pay the $1400 and up that the original non-lock 610s seem to command these days.
Your .30 carbine AMT was the other version of the Automag III - the 9mm Win mag and the 30 carbine cartridge are close enough dimensionally that the same magazine is used for both (with maybe a slight difference in the feed lips), and they were all "long-slide" models. The Automag IV came in .45 Win mag and 10mm Win Mag. I also carried an AMT backup in .380 auto for a while many years ago as my CCW. Then I upgraded to a Colt mustang pocketlite for a while, and now various Kel-Tecs fill the extremely small CCW role for me. My most compact .45 ACP is an old Republic Arms Patriot, which is a very well-made small .45 with DAO and no other external controls. Unfortunately, after the company sold out to Cobra, the quality really went down, and I can't really recommend the Cobra version of the Patriot. According to my sources, the Patriot is why George Kelgren (the engineer behind Grendel and Kel-Tec) never came out with a .45 ACP Kel-Tec - he didn't think that he could improve on the Patriot design.
I suspect that we could spend many hours discussing firearms, as it appears that we have many common interests - but this forum is probably not an appropriate place for it...