Light gathering capability difference between a 50 and 40 is night and day though...literally. To each his own. They'll both kill a deer, so to each his own I guess.
Leupold engineer told me all other things equal, difference from 40mm to 50mm is 1-2% more. Most say yer eyes can't detect that small amount. It's the quality of glass, number of lenses , polish and such that makes a scope.
I don't own any over 40mm, prolly never will.
