First, of all... Welcome to the forum. This is the right place to be.
My Pietta takes .454 balls best
When you load the revolver, one of the things the ball does for you is to help seal the wall of the chamber to prevent hot gas from the discharged chamber from getting past the bullet and into the powder in the chambers which are not in line with the barrel.
To make sure this seal is as good as it can be, shooters like to observe a complete ring of lead that is shaved off the the bullet as the bullet is rammed into the chamber.
The ball should be large enough that you get a complete ring.
In addition, the ball has to thoroughly engage the rifling of the barrel. The groove diameter of your barrel should be somewhere around .446, so I am thinking that either ball will engage the rifling successfully. The Chamber diameter is right at .450.
But think about it. At .451, the most that the chamber will shave off the ball is .001 but at .454, you are shaving off .004. This shaving action actually takes the ball which starts out as a sphere creates a flat band all the way around the bullet. This flat area creates more surface for the bullet to engage the rifling.
Other members will very likely wade in with data from a scientific comparison of .451 performance as measured against .454 performance. I never did a comparison of bullet speed nor have I noted much difference in accuracy because I am not that good of a shot.
To me it all boils down to the lead ring.
My reading of history convinces me that most bad government results from too much government. Thomas Jefferson