I will throw this in to complicate things.

You asked about a .45 or a .500, why not go halfways and consider a .475 Linebaugh...

Any of those fine gunsmiths mentioned can build you one.

In my humble opinion, the .475 will do anything the .500 will do and may even penetrate better (not that you may ever need it.)

Mine has worked great on several big mule deer (of course its way over-kill) and 2 mature bull elk (complete penetration); and should I ever go for a big bear, it will be my primary choice.

Not sayin' the .500 won't (or even the .45 Colt,) just trying to muddy the waters a bit for discussion.

PS: Whit, your photos are excellent of your guns, I know it ain't that easy...