"Something else to remember is that contrary to common belief, a larger objective lens does not increase the field of view of a riflescope. It only increases the amount of light entering the scope, and, in the case of scopes using slightly less capable components, it will increase the “sweet spot” at the optical center of the lens, making images appear sharper and more crisp in the center of the field of view."
This is correct, objective size has nothing to do with FOV. It's a common mistake that is often made, most likely, because at a glance it's just so darn easy to assume bigger objective means greater FOV, but it doesn't work that way.
Where a 50 shows its benefit is when you are using the upper ends of the magnification range, at that point the bigger 50's or even 56's show their advantage but if you typically don't use the higher end of the magnification range, their is no advantage to a 50 over a 40, with everything else being equal.
As for 30mm versus 1 inch tube, in all honesty, it's a lot of marketing and really the biggest thing a 30mm offers over a 1in. is more vertical adjustment but if you don't plan on dialing up for extended range shots, and lets be honest here, I don't know anyone that dials for elevation using a scope with caps and no external adjustments so what's the point of all these 30mm scopes with caps.
To the OP, before I decided on going with a 40 or a 50 I would first decide on what is the $$$ amount I wanted to spend, then I would try and get the very best glass/optics I could get for the $$$ cap I set for myself. I'm sure others will have a differing opinion but for me, optic quality trumps everything else.
