Re: 50 or 56 that is the queston
I have both. It is very difficult to tell any difference in 99% of use.
The one place I can see a difference is in shaded dawn or dusk use. I have a location that I use to hunt bobcats and coyotes that is in wooded cover. If I crank the zoom up, say past 10x, I can tell the difference. It isn't a lot but it is there. I can still make the shot with either.
I have two different sizes because I was in your shoes at one time. They had a 50 and not a 56 and I am impatient and I bought it. I have no regrets.