I enjoy my .45 Colt Handi, but not more than a lot of others. What's your fixation on the .45 Colt. Do you want to match it to a handgun? You mention .45ACP, so I guess not. If you want a pistol caliber carbine that really works, and save a bunch of money, I'd get a .357 and ream it to Maximum. It shoots a lot cheaper (read more range and hunting time) and you can chop it back as far as 16 inches and it'll still shoot anything you can feed it.
The .45-70 has been mentioned, and you can't beat it. As my friend George Mann (jeepmann1948) just said a moment ago on the phone, why not the .44 mag. It'll do all you want, barrels are available plus a wider range of bullets.
Just some thoughts,
Pete