This is almost too narrow a survey to answer. I, like WlScott answered other. Not only is where I am hunting relavent, but what gun and load I am using. The average 308/30-06 load or close equvilent (270,280,303 Brit, 7x 57 etc) can be sighted 2" high at 100 and be very close to either point of aim or 2-3" low at 200, and this is probably a perfect sightin range for a great many shooters. But what should really dictate the sight in distance is the point blank range of the load or your max expected range. Following this, I generally use a point blank target size of 4". This will let the bullet rise and fall 2" above/below line of sight. For my 45-70 using a 400 grain bullet at 1500 fps, this is about 125 yards. For my 30-30 driving The Hornady 150 SST at 2360 fps, the 4" point blank range is 200 yards. My 44 Mag and 357 Max I sight in at 75 yards, I use them both strictly as woods guns and want them to be as flat as reasonable and still be able to hold dead on at 100.
Shotguns with slugs and muzzleloaders using modern sabot loads are quite similar in trajectory to the 45-70 and 150 yards is a long shot with these guns. Maximum point blank range of a load may or may not fall within the size of the kill zone. Every load is different and I don't think there is a one size fits all, and while every shooter may have a "zero" range they prefer, that they know why they have chosen that range and how the bullet will travel before and after it are far more important than what the given range is.