If you want more light during the early morning or late evening hours all you have to do is reduce the magnification SLIGHTLY and you won't need to bother with a 56mm objective lens.
Example: It is generally accepted that the human eye can not use a column of light larger than about 6mm. (even smaller for older eyes) You will get a 6mm column of light from a 56mm objective with the magnification set @ 9.3x. Using an identical scope with a 50mm objective lens you would have to use a magnification of 8.3x to get the same column of usable light. How much difference would it make if your scope was set on 8x rather than 9x? Virtually none, and you wouldn't have to deal with the weight, height or cost of a 56mm scope.
I might add that there is nearly as strong an argument for staying with scopes that have a 44mm objective. Same amount of usable light @ 7.3x. Personally, I have no problem with 40mm-44mm objectives.
Just my 2 cents and I've got 40mm's, 44mm's, 50mm's and a single Nightforce 12x42x56.