Re: 40mm or 50mm Objective
I'd take a 40mm or 42mm scope over a 50mm anyday, my main reason for this is that with a lower mounted scope it makes quicker to get your crosshair on the target, and you head is in a more comfortable shooting position (If you have an ajustable cheak piece on you stock this dosen't matter).
My 2 cents
Old aunts used to come up to me at weddings, poking me in the ribs & cackling "You're next". They stopped after I started doing the same thing to them at funerals.