The highest magnification I've ever used on a hunting rifle are the Burris 3-9X40's that are on my Remington Classic .220 Swift and my Ruger 77 .280. In the field, both rifles scopes are kept set on 3 or 4X. The longest shot I ever made on big game was a smidge over 350 yds. on a bull elk. The rifle was my .35 Whelen and its scope is a Burris 4X Fullfield. My heavily used Scout Rifle in .308 wears a 2.75X Scout Scope. Between my oldest daughter and I, we've killed a truck load of game with it, never once wishing for magnification. My dad has always been a fan of 1.5-5X scopes, but when he got in his '70's found he needed a little more magnification for his aging eyes and switched to a 2-7X40.
Higher magnification scopes can be a bane, and I've lost count of the number of my buddies who missed shots on game because "....dangit....I jumped a buck, but I forgot to turn the magnification down and couldn't find him in the scope.". A 4X scope at 25 yds. has a field of view of around 7'. At the same distance a 9X scope has a FOV of around 3.5', and a 12X around 2'. The glass manufacturers have done a great job in convincing us that more magnification and objective lenses the size of trash can lids are better and I just have to shake my head in disbelief when I see hunting rifles, especially the light, trims ones, that appear to have been mounted to the scope, rather than the scope having been mounted to them. The up side to this is that quality, used 4X scopes are readily available at good prices.
35W