RE: Scope Size
I use a 3x9x50, it's better than a 3x9x40.
If you can afford it, I would get a Bushnell Elite 4x12x50, that's a good scope. Of course, you will need to tell us what caliber of gun you are using.
The Bushnell Elite I just mentioned is good for .30 caliber (Not Magnums) and under.