Let's see... I want a big bore back-up .475 or .50 cal. stopping handgun but only if it has a 4 3/4 " barrel and I can shoot it one handed.... UH- huh ! It keeps gettin' better and better. In light of all this, I recommend a .500 S&W with the barrel custom cut to 4 3/4", no compensator, and the hammer bobbed off. That way it can be shot double action only.
Hatari, as I responded on Sixgunner.com, buy the .475. Forget about using one hand until you're thoroughly experienced with the gun, after many hundreds or thousands of rounds, and then only when the buff has blood streaming from his nose, his horns are down and he's 10 yards away and coming fast. Better yet, kill him at 50 yards. With 2 hands, and the 420 gr. bullet in the right place.