RE: OK. Decision Time. 3x9x40 or 3x9x50, Which is better?
Depends on the scope. A good scope shouldn't need a 50 mm objective to have good light transmission. At least not in hunting powers. I don't even have a 50 on my 20 power varmint scope.
It may help with feild of view at higher powers though.
It will also make you mount your scope higher as well.
Honestly with a quality fully coated lens scope a 32 mm objective should work just fine in legal hunting hours, even in the shade.
Now if your talking a sub 100 dollar scope like a BSA or tasco or something you may notice a difference with a bigger objective. I bet it still won't be as clear as a scope for twice that price with half the size objective though.
My opinion anyway.
Paul