I would choose the 404
You can have the rifle built on a smaller action and have the option of the regular 400grain bullets or the new 450grain woodleighs (available in Norma ammunition if you don't reload). I also prefer the .423 diameter bullets compared to the .416, but whether it makes a significant difference or not is another matter... Of course if you go with the 416, then 450 grain woodleighs are also available for that now too.

Did you decide on a rifle maker?