I have one of each also, a 455 American and a 452 Varmint. The 452, other than a lighter trigger spring and a striker reshape, is bone stock. The 455 has pillars, epoxy bedding, lighter trigger, and finally a striker reshape. After all that, it does shoot better than original, but not as well as the 452.
Having said that, they ARE two different rifles, not apples to apples.
This target was shot on the same day, same ammo, same shooter at 50 yds. The top row is 452, bottom is 455. The 4th group with the 452 is all about me.. It's what happens when you get excited and forget how to shoot .. my bad. Both rifles throw a flyer on the first shot out of a cold barrel, those are seen in the first group shot with each rifle.
All that's keeping the 455 in my safe right now is a gorgeous tiger striped walnut stock. I doubt I'll ever sell it for that reason alone. It's a good shooter in its own right, but not in the same sense as the 452 Varmint.

Neither rifle has given me a lick of trouble, both function flawlessly and are well made. Anyone other than a paper punching accuracy junkie like me would be thrilled to have either one.
Great rifles for the money if you ask me.