Perhaps I should be more specific. Width versus weight. The Merkel weighs in at 9.8 lbs but is very narrow compared to the Jeffery, which is damn wide. Also the Jeffery has a 28" bbl making it feel heavier that is is. No, I don't want to whack them off

So, I'll agree that 11-12 lbs is just right for a 450, I'd say that 10 lbs would be perfect for a 450/400.

I've never shot a 500 or 577 and have not clue what they should weigh.

Funny think about weight is the Ying & Yang. A light rifle is easy to carry and a heavy one absorbs recoil. I doubt this will be the last we hear of this topic.