On different days, my American might beat the Varmint.
The American is for carrying; The Varmint is for lying down beside and shooting gophers.
Considerable Ammunition research is required: Pillar Bedding, Firing pin reshaping, a heavier spring, a YoDave trigger kit and finding the scope that meets your needs are areas to be considered.
Since the 455's are designed to fire long rifle and by switching the barrels you can go to magnum rimfires I bought into the theory. Working with a chronograph might show improvements
Reshaping the firing pin should give better ignition. The reshaping creates a strike inside the outer part of the rim versus crushing brass that is the make up of the outer rim.
These strikes show what is desired:

There are so many variables and finding the correct one(s) might not happen quickly if ever.
Recently I read an article about lapping the barrel and you can accomplish that by shooting 300 lead bullets and cleaning after every 100. Lead only, no copper washed, and brand of lead bullets makes no difference. Will you ruin your barrel shooting copper . . . I don't know but perhaps I read the article after shooting lead and MiniMags.
The difference between a 5 pound trigger and something around one pound is huge.
Many will advocate a 2 - 7 power scope. That is okay if you limit your shots to short range.
Try 3-9, 4-12, 4.5 - 14, 6 - 18, and 2.5 to 16 which where I am at with my American. The Varmint wears a 4.5-14. What is a reasonable criteria as to how much power you need and how much field of view suits your needs. Seeing a gopher's eye and being able to make a head shot given the limits of the ammunition pretty much answers my needs.
On any given day the American may outperform the Varmint. While I regard them both as gopher guns the experimenting continues. Both rifles have shot under an inch at 100 yards. Stretching the range out to 200 doubles the pleasure . . . doubles the fun.