I do think that in this day and age (and always for that matter) that the 450 is a much more versatile rifle when it comes to bullet types and weights to try as you well know from your own experience.
In fact, although not the 450 3-1/4”, when Holland & Holland touted the accuracy of their 500/450 nitro all of the superior groups were shot using their 365gr bullet in rifles very likely regulated for the 480gr bullet.
And that, gentlemen, is where the much lauded (and believed to be modern) idea of the 75% rule came from.

Also, another welcome to NitroExpress and we look forward to your reports not only on the 450 but on your other two doubles.