You are starting with a question which is, at best, about 4 down on the list one should be addressing.
For me personally, as far as it is to the gun store door. I don't like 7mm Mags - except there was that one Husquavarna......and I know where it lives...
Anything a 7 Mag can do for all practical purposes, an '06 can do just as well, and a 300 mag will do it better.
But to each his own.... Just answer the following questions:
1. How well can the rifle in question shoot ( benchrest)? 2 inch groups are generally sufficient for most hunters, 3 inches are just acceptable - they can generally be improved on with glass-bedding and a trigger job. Circa 1 inch or less is pure gravy.
2. How well can the shooter shoot (various field positions, with and without rests)?
3. What's the range- how well can the shooter estimate? - better yet- does he have a range-finder and the time to use it when the game is "out there"?
Been a pile of game killed by sighting in the rifle (any reasonable caliber) at 2.5 to 3 inches high at 100 (assuming decent 2" or less groups), getting a good rest when crunch time comes, and taking the shot when offered. Believe me- a 300 yard distant animal is a LONG ways away, but it is still virtually a point-blank shot ballistically for the rifle if above conditions are met. Just hold on hair, but slightly high when way out there. The ballistics of the particular rifle are the least of your worries- though you need to know them- when shooting way out there.
Accurate ranging is paramount beyond 300 yards, as your bullets are dropping like a rock out there past 300 yards or so, with any caliber. Still perfectly capable of clean kills- the major problem is getting the bullet where it need go! Hence the accurate ranging via range-finders. Your eyes just aren't equal to a good laser rangefindere - and 20 yards makes a difference beyond 300 yards or so.
