Given all the "improvements" they have made on the 455, you would still choose the 452 based on the sight along?
The sights on the 452 are superior. I wish they put the same style of sights on the 455 that they used on the 452. The 452 style sights are the best facotry sights out there.
Right now, I am not a "caliber swapper". I don't know if I would call them "improvements", I would just call it "simplified manufacturing". If given the choice, and the prices were similar, I would go with the 452. The 455 will be around for years to come and easy to get. The 452's, not so.
If bench or strictly varmint shooting, I might go with a varmint over the American if buying today. Had a varmint at one time, my American shot better. Don't have the varmint anymore. Also have 2 trainers. They both shoot better than my American.