".......So.. it seems to me like the 450 NE is a more powerful cartridge than the 450/400 3"...."
As Sherlock Holmes said: Elementary my dear Watson.....bigger heavier bullet at roughly same velocity = more energy. You can read the numbers right off the ammo boxes.

Just curious; if you already have and are familiar with .416 Rigby, .458 Lott, .375 H&H, 9.3x74, and a .470 (is the .470 more powerful than the 9,3x74?

) you could use the internet, Google Search, Taylor Knock Out values, and/or Wikipedia to learn the details of .450 NE versus .450/.400 3".