The 9" analogy is a good one - pie plates used for testing this also work as they can be painted to be visible ---- something animal's colouration lacks.

In my own testing, I've proven I'm OK with my open sighted rifles, to 200yards - including the 9.3x57 (moose in 2009 exactly 200yards - impact right on the bead=perfect), .45/60 Sharps w/405RP's or 500gr. RN cast and my .69 smoke-pole with 480gr. RBs. All the rest have scopes. That 200ard moose shot was the second longest shot ever taken by me with any rifle on big game, scope or otherwise. Most are inside 100yards - scope or open sights, and many inside 60 yards.

Much depends on where you hunt.