I also think you should consider the 2x-7x 32 Pro Staff. It is a really good scope for the money. Holds Zero and clear for the $.2x really helps in the thick stuff. 7x great for targets.

I am not sure but isnt the prostaff a 4x32 and the buckmaster a 4x40?
If you are set on a fixed 4x go 40mm without a doubt.

Ihave heard great things about the weaver k4 but can not comment for lack of personal experience.