"To start with what is the maximum distance that you want the bullet to be above or below the line of sight?"
In addition to this, HOW MUCH above & below the LOS do you desire? This is based on the game you plan to shoot! For deer, I don't want the bullet to be much over 4" above or below the center hold. But for an elk or moose, you can at least double that and still make a vital hit using a center hold!
And, as stubblejumper says, you have to know the MV and ballistic coefficient of your ammo/rifle combination, plus the distance from the center of the bore to the optical centerline of your scope.
When you have this information, go to
http://www.handloads.com/calc/and play with the zeroing distances to get the figures you are looking for.
BTW, barrel length is not germaine to this particular question.
You MUST KNOW the actual, exact MV of the load you are firing regardless of barrel length.