Actually, the Remington 1858 is one of the most powerful. It's ballistics are equivalent to a .45ACP and although the Walker is significantly more powerful, it is hard to reload and carry because of the weight.
With the Remington, you have 6 full powered rounds in the rather light and portable gun, and you can easily change the cylinder for more ammunition. An experienced gunfighter can change cylinders in a few seconds and have a fresh 6 rounds. So the Remington is power plus manueverability, while the Walker is merely power.