In todays world the 470 is the way to go.
However I would not trade my 450 No2 for an identical rifle in 470. The 450 No2 is one of the easiest Nitro cases to load for. Its shape is perfect, it has a thick strong rim. Also I like the .458 Bore and the bullets avaialable.
As far as effectiveness on game I do not think there is any difference in the Nitro Expresses from the 450 through the 475's.