Re: Nightforce 56mm -vs- 50 mm
Mathematically, the 56mm is brighter.
To the human eye you would likely notice nothing. You are splitting hairs at this point. You will notice the difference in weight and bulk and profile when carrying and handling the rifle for sure.
After having 4 56mm and a couple of 50's, I will never look back to the 56's. The weight, profile and bulk does not justify the mathematical light transmision gain.
A die hard 56mm fan will tell you other wise but it will boil down to how much more you are willing to carry for how little performance gain.
As it is, the 50mm will gather enough light to get you into serious trouble with the game and fish before sunrise and after sunset.
Long range shooting is a process that ends with a result. Once you start to focus on the result (where the shot goes, how big the group is, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.