I know that the 3x-9x is the standard big game hunting magnification range, but I find the 4x-12x to be ideal - especially on longer shots. For whatever reason, I seem to shoot tighter groups at big game when the magnification is higher. As for the 40mm to 50mm debate, I really like 50s over the 40s (all else being equal).
The Nikon Buckmasters are great scopes for the money. Combine that with the 4x-12x-50mm model, well....heck, I think that I just may buy one! :grin:
Zachary