Love vortex scopes all styles are greatAn then there is the issue of FFP scopes where if you are using low power the reticle can get so fine that it is hard to see in the woods, where a SFP reticle is always the same size regardless of the power setting. I have a Vortex Viper 6-24x50. The reticle is quite fine at 7power (still bright at that power) and is very fine at 24power. I would say that SFP scopes are better for hunting than FFP because the reticle is easier to see in very low light. In my experience, only the Trijicon small lighted dot is useful during twilight in the woods. Just my view...
Yeah, the FOV has little or nothing to do with the objective lens size. Indeed the March site shows the 42 and 52 both have the same FOV at 25X: 4.3feet.Currently running 2 March 2.5-25x52 and love them. The only downside to them is FOV at 25 power. I believe the 42 would be even less FOV. Also have heard the eyebox is finicky on the 42. For those reasons I would suggest the 52.
If memory serves, the March 50X had a 52mm objective. You're comparing that to an NF 12-42X56, which has a lower magnification and a larger objective.Check both under low light conditions. My March 50X fixed is a GREAT scope, but very dark in low light. Both my NF 12-42BR and Weaver 48X are brighter in low light.
My experience is with two March 2.5-25x42mm scopes. As others have said the eye box is tight. I found that by focusing the cross hairs before mounting the scope and setting the magnification to 25 while adjusting the position of the scope in the rings for eye relief reduced the eye box affect dramatically.